Doc test: check condition for building the docs with Sphinx

Sphinx will attempt to fetch the Python objects inventory during the build
process. If for some reason, this test is being run on a machine that can
not access that address simply because of network restrictions (or the
developer may simply be on a plane) then it's better to SKIP the test than
to give a false positive.

Changes from v0:
 * Use unittest2 on Python 2.6
Signed-off-by: NCleber Rosa <crosa@redhat.com>

selftests/doc/test_doc_build.py

@@ -5,7 +5,12 @@ This is geared towards documentation build regression testing.
 """
 import os
 import sys
-import unittest
+import urllib
+
+if sys.version_info[:2] == (2, 6):
+    import unittest2 as unittest
+else:
+    import unittest
 
 from avocado.utils import process
 
@@ -18,8 +23,26 @@ class DocBuildError(Exception):
     pass
 
 
+def has_no_external_connectivity():
+    """
+    Check condition for building the docs with Sphinx
+
+    Sphinx will attempt to fetch the Python objects inventory during the build
+    process. If for some reason, this test is being run on a machine that can
+    not access that address simply because of network restrictions (or the
+    developer may simply be on a plane) then it's better to SKIP the test than
+    to give a false positive.
+    """
+    try:
+        urllib.urlopen('http://docs.python.org/objects.inv')
+        return False
+    except:
+        return True
+
+
 class DocBuildTest(unittest.TestCase):
 
+    @unittest.skipIf(has_no_external_connectivity(), "No external connectivity")
     def test_build_docs(self):
         """
         Build avocado HTML docs, reporting failures
@@ -52,3 +75,7 @@ class DocBuildTest(unittest.TestCase):
             e_msg += ('Full output: %s\n' % '\n'.join(output_lines))
             e_msg += 'Please check the output and fix your docstrings/.rst docs'
             raise DocBuildError(e_msg)
+
+
+if __name__ == '__main__':
+    unittest.main()