[vstest]: print output when runcmd returns error (#672)

* [vstest]: print output when runcmd returns error

Signed-off-by: Guohan Lu <gulv@microsoft.com>

tests/conftest.py

@@ -123,7 +123,14 @@ def destroy(self):
  ensure_system("ip netns delete %s" % self.nsname)
 
  def runcmd(self, cmd):
- return os.system("ip netns exec %s %s" % (self.nsname, cmd))
+ try:
+ out = subprocess.check_output("ip netns exec %s %s" % (self.nsname, cmd), stderr=subprocess.STDOUT, shell=True)
+ except subprocess.CalledProcessError as e:
+ print "------rc={} for cmd: {}------".format(e.returncode, e.cmd)
+ print e.output.rstrip()
+ print "------"
+ return e.returncode
+ return 0
 
  def runcmd_async(self, cmd):
  return subprocess.Popen("ip netns exec %s %s" % (self.nsname, cmd), shell=True)
@@ -294,6 +301,11 @@ def runcmd(self, cmd):
  except AttributeError:
  exitcode = 0
  out = res
+ if exitcode != 0:
+ print "-----rc={} for cmd {}-----".format(exitcode, cmd)
+ print out.rstrip()
+ print "-----"
+
  return (exitcode, out)
 
  def copy_file(self, path, filename):