[test][test_brb] Gate the test behind the new skipUnlessHasBinaries d…

…ecorator

If we have the binaries on file, we should fail and report the failure.
Currently, if the binaries are missing, the test fail and we just ignore it.
If the binaries are there and we fail, we would have the same outcome, but
really, we should report the failure as something wrong would have happened.

Faking a missing binary:
```
$ docker run -ti \
                    --privileged \
                    --network=host \
                    --pid=host \
                    -v $(pwd):/bcc \
                    -v /sys/kernel/debug:/sys/kernel/debug:rw \
                    -v /lib/modules:/lib/modules:ro \
                    -v /usr/src:/usr/src:ro \
                    -e CTEST_OUTPUT_ON_FAILURE=1 \
                    u34 \
                    /bin/bash -c \
                    '/bcc/build/tests/wrapper.sh "py_test_percpu" "sudo" "/bcc/tests/python/test_brb.py" test_brb.c -v'
test_brb (__main__.TestBPFSocket) ... skipped 'Missing binaries: iper, neterf. iperf and netperf packages must be installed.'

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK (skipped=1)
```

running against a container where both iperf and netperf were installed:

```
net.ipv4.ip_forward = 1
ARPING 100.1.1.254
42 bytes from b2:55:dc:a4:58:81 (100.1.1.254): index=0 time=8.384 usec

--- 100.1.1.254 statistics ---
1 packets transmitted, 1 packets received,   0% unanswered (0 extra)
rtt min/avg/max/std-dev = 0.008/0.008/0.008/0.000 ms
ARPING 200.1.1.254
42 bytes from 9e:94:6c:ba:2a:3c (200.1.1.254): index=0 time=8.918 usec

--- 200.1.1.254 statistics ---
1 packets transmitted, 1 packets received,   0% unanswered (0 extra)
rtt min/avg/max/std-dev = 0.009/0.009/0.009/0.000 ms
PING 200.1.1.1 (200.1.1.1) 56(84) bytes of data.
64 bytes from 200.1.1.1: icmp_seq=1 ttl=63 time=0.097 ms
64 bytes from 200.1.1.1: icmp_seq=2 ttl=63 time=0.079 ms

--- 200.1.1.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1019ms
rtt min/avg/max/mdev = 0.079/0.088/0.097/0.009 ms
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0- 1.0 sec  6.46 GBytes  55.5 Gbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0- 1.0 sec  6.46 GBytes  55.0 Gbits/sec
Starting netserver with host 'IN(6)ADDR_ANY' port '12865' and family AF_UNSPEC
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 200.1.1.1 () port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072  16384  65160    1.00     49468.46
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 200.1.1.1 () port 0 AF_INET : demo : first burst 0
Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384  131072 1        1       1.00     63173.69
16384  131072
ok

----------------------------------------------------------------------
Ran 1 test in 9.331s

OK
```

Forcing a failure when all binaries are on the system:
```
net.ipv4.ip_forward = 1
ARPING 100.1.1.254
42 bytes from 62:d8:ac:1e:d4:ee (100.1.1.254): index=0 time=5.247 usec

--- 100.1.1.254 statistics ---
1 packets transmitted, 1 packets received,   0% unanswered (0 extra)
rtt min/avg/max/std-dev = 0.005/0.005/0.005/0.000 ms
ARPING 200.1.1.254
42 bytes from 42:07:f7:d5:d2:b9 (200.1.1.254): index=0 time=6.799 usec

--- 200.1.1.254 statistics ---
1 packets transmitted, 1 packets received,   0% unanswered (0 extra)
rtt min/avg/max/std-dev = 0.007/0.007/0.007/0.000 ms
PING 200.1.1.1 (200.1.1.1) 56(84) bytes of data.
64 bytes from 200.1.1.1: icmp_seq=1 ttl=63 time=0.104 ms
64 bytes from 200.1.1.1: icmp_seq=2 ttl=63 time=0.084 ms

--- 200.1.1.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1000ms
rtt min/avg/max/mdev = 0.084/0.094/0.104/0.010 ms
FAIL

======================================================================
FAIL: test_brb (__main__.TestBPFSocket)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/bcc/tests/python/utils.py", line 68, in wrapper
    func(self, *args, **kwargs)
  File "/bcc/tests/python/test_brb.py", line 201, in test_brb
    self.assertEqual(self.pem_stats[c_uint(0)].value, 9)
AssertionError: 8 != 9

----------------------------------------------------------------------
Ran 1 test in 4.294s

FAILED (failures=1)
```

tests/python/test_brb.py

@@ -65,7 +65,7 @@
 from netaddr import IPAddress, EUI
 from bcc import BPF
 from pyroute2 import IPRoute, NetNS, IPDB, NSPopen
-from utils import NSPopenWithCheck, mayFail
+from utils import NSPopenWithCheck, skipUnlessHasBinaries
 import sys
 from time import sleep
 from unittest import main, TestCase
@@ -147,7 +147,9 @@ def config_maps(self):
  self.br1_rtr[c_uint(0)] = c_uint(self.nsrtr_eth0_out.index)
  self.br2_rtr[c_uint(0)] = c_uint(self.nsrtr_eth1_out.index)
 
- @mayFail("If the 'iperf', 'netserver' and 'netperf' binaries are unavailable, this is allowed to fail.")
+ @skipUnlessHasBinaries(
+ ["arping", "iperf", "netperf", "netserver", "ping"],
+ "iperf and netperf packages must be installed.")
  def test_brb(self):
  try:
  b = BPF(src_file=arg1.encode(), debug=0)