[pytest]: print out stdout/stderr message when cmd fails (#1188)

tests/conftest.py

@@ -14,9 +14,9 @@
 from swsscommon import swsscommon
 
 def ensure_system(cmd):
-    rc = os.WEXITSTATUS(os.system(cmd))
+    (rc, output) = commands.getstatusoutput(cmd)
     if rc:
-        raise RuntimeError('Failed to run command: %s' % cmd)
+        raise RuntimeError('Failed to run command: %s. rc=%d. output: %s' % (cmd, rc, output))
 
 def pytest_addoption(parser):
     parser.addoption("--dvsname", action="store", default=None,
@@ -214,7 +214,7 @@ def __init__(self, name=None, imgname=None, keeptb=False, fakeplatform=None):
 
             # mount redis to base to unique directory
             self.mount = "/var/run/redis-vs/{}".format(self.ctn_sw.name)
-            os.system("mkdir -p {}".format(self.mount))
+            ensure_system("mkdir -p {}".format(self.mount))
 
             self.environment = ["fake_platform={}".format(fakeplatform)] if fakeplatform else []
 
@@ -385,15 +385,15 @@ def get_logs(self, modname=None):
         else:
             log_dir = "log/{}".format(modname)
         os.system("rm -rf {}".format(log_dir))
-        os.system("mkdir -p {}".format(log_dir))
+        ensure_system("mkdir -p {}".format(log_dir))
         p = subprocess.Popen(["tar", "--no-same-owner", "-C", "./{}".format(log_dir), "-x"], stdin=subprocess.PIPE)
         for x in stream:
             p.stdin.write(x)
         p.stdin.close()
         p.wait()
         if p.returncode:
             raise RuntimeError("Failed to unpack the archive.")
-        os.system("chmod a+r -R log")
+        ensure_system("chmod a+r -R log")
 
     def add_log_marker(self, file=None):
         marker = "=== start marker {} ===".format(datetime.now().isoformat())