ustat: Replace \0 with spaces in cmdline

The /proc/PID/cmdline file has \0 for spaces in the command
line, and there may be trailing \0 characters as well.
Replace them all with spaces.

tools/ustat.py

@@ -55,7 +55,7 @@ def _find_targets(self):
  comm = open('/proc/%d/comm' % pid).read().strip()
  if comm in self.procnames:
  cmdline = open('/proc/%d/cmdline' % pid).read()
- self.targets[pid] = cmdline
+ self.targets[pid] = cmdline.replace('\0', ' ')
  except IOError:
  continue # process may already have terminated
 
@@ -220,8 +220,9 @@ def _loop_iter(self):
  print()
  with open("/proc/loadavg") as stats:
  print("%-8s loadavg: %s" % (strftime("%H:%M:%S"), stats.read()))
- print("%-6s %-16s %-10s %-6s %-10s %-8s %-8s %-10s" % ("PID", "CMDLINE",
- "METHOD/s", "GC/s", "OBJNEW/s", "CLOAD/s", "EXCP/s", "THREAD/s"))
+ print("%-6s %-20s %-10s %-6s %-10s %-8s %-6s %-6s" % (
+ "PID", "CMDLINE", "METHOD/s", "GC/s", "OBJNEW/s",
+ "CLOAD/s", "EXC/s", "THR/s"))
 
  line = 0
  counts = {}
@@ -235,8 +236,8 @@ def _loop_iter(self):
  else:
  counts = sorted(counts.items(), key=lambda (k, _): k)
  for pid, stats in counts:
- print("%-6s %-16s %-10d %-6d %-10d %-8d %-8d %-10d" % (
- pid, targets[pid][0:16],
+ print("%-6d %-20s %-10d %-6d %-10d %-8d %-6d %-6d" % (
+  pid, targets[pid][:20],
  stats.get(Category.METHOD, 0) / self.args.interval,
  stats.get(Category.GC, 0) / self.args.interval,
  stats.get(Category.OBJNEW, 0) / self.args.interval,