qemu-iotests: iotests.VM: remove qtest socket on error

On error, VM.launch() cleaned up the monitor unix socket, but left the
qtest unix socket behind. This caused the remaining sub-tests to fail
with EADDRINUSE:

+======================================================================
+ERROR: testQuorum (__main__.TestFifoQuorumEvents)
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "148", line 63, in setUp
+    self.vm.launch()
+  File "/home6/silbe/qemu/tests/qemu-iotests/iotests.py", line 247, in launch
+    self._qmp.accept()
+  File "/home6/silbe/qemu/tests/qemu-iotests/../../scripts/qmp/qmp.py", line 141, in accept
+    return self.__negotiate_capabilities()
+  File "/home6/silbe/qemu/tests/qemu-iotests/../../scripts/qmp/qmp.py", line 57, in __negotiate_capabilities
+    raise QMPConnectError
+QMPConnectError
+
+======================================================================
+ERROR: testQuorum (__main__.TestQuorumEvents)
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "148", line 63, in setUp
+    self.vm.launch()
+  File "/home6/silbe/qemu/tests/qemu-iotests/iotests.py", line 244, in launch
+    self._qtest = qtest.QEMUQtestProtocol(self._qtest_path, server=True)
+  File "/home6/silbe/qemu/tests/qemu-iotests/../../scripts/qtest.py", line 33, in __init__
+    self._sock.bind(self._address)
+  File "/usr/lib64/python2.7/socket.py", line 224, in meth
+    return getattr(self._sock,name)(*args)
+error: [Errno 98] Address already in use

Fix this by cleaning up both the monitor socket and the qtest socket iff
they exist.

Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Reviewed-by: Bo Tu <tubo@linux.vnet.ibm.com>
Message-id: 1459848109-29756-4-git-send-email-silbe@linux.vnet.ibm.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/iotests.py

@@ -16,6 +16,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
+import errno
 import os
 import re
 import subprocess
@@ -247,7 +248,8 @@ def launch(self):
             self._qmp.accept()
             self._qtest.accept()
         except:
-            os.remove(self._monitor_path)
+            _remove_if_exists(self._monitor_path)
+            _remove_if_exists(self._qtest_path)
             raise
 
     def shutdown(self):
@@ -409,6 +411,15 @@ def complete_and_wait(self, drive='drive0', wait_ready=True):
         event = self.wait_until_completed(drive=drive)
         self.assert_qmp(event, 'data/type', 'mirror')
 
+def _remove_if_exists(path):
+    '''Remove file object at path if it exists'''
+    try:
+        os.remove(path)
+    except OSError as exception:
+        if exception.errno == errno.ENOENT:
+           return
+        raise
+
 def notrun(reason):
     '''Skip this test suite'''
     # Each test in qemu-iotests has a number ("seq")