usdt.py: print errors to stderr in enable_probe_or_bail()

src/python/bcc/usdt.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import print_function
 import ctypes as ct
 import os, sys
 from .libbcc import lib, _USDT_CB, _USDT_PROBE_CB, \
@@ -160,7 +161,7 @@ def enable_probe_or_bail(self, probe, fn_name):
  try:
  self.enable_probe(probe, fn_name)
  except USDTException as e:
- print(e)
+ print(e, file=sys.stderr)
  sys.exit(1)
 
  def get_context(self):