python: tests: Allow some tests to be skipped.

Currently test820RHBZ912499.py fails with libvirt because libvirt
still doesn't work around qemu locking properly.  Allow this test to
be skipped on a temporary basis using SKIP_TEST820RHBZ912499_PY=1

python/t/test820RHBZ912499.py

@@ -30,6 +30,7 @@ from .tests_helper import *
 
 
 # If the architecture doesn't support IDE, skip the test.
+@skipIfEnvironmentVariableSet("SKIP_TEST820RHBZ912499_PY")
 @skipUnlessArchMatches("(i.86|x86_64)")
 @skipUnlessGuestfsBackendIs('libvirt')
 @skipUnlessLibvirtHasCPointer()

python/t/tests_helper.py.in

@@ -18,6 +18,7 @@
 
 # Utilities for the tests of the Python bindings.
 
+import os
 import sys
 import unittest
 
@@ -28,6 +29,16 @@ else:
     int_type = long
 
 
+def skipIfEnvironmentVariableSet(name):
+    """
+    Skip the current class/method if the named environment variable
+    is set to 1
+    """
+    if os.environ.get(name, "") == "1":
+        return unittest.skip("skipped by environment variable")
+    return lambda func: func
+
+
 def skipUnlessConfiguredWithLibvirt():
     """
     Skip the current class/method if ./configure --without-libvirt