trap errors from git not being present

subprocess raises OSError if the command it is asked to run isn't found,
so trap that as well as the subprocess-specific error we were already
catching.

Change-Id: Ieb9c7f3ccc307250847104a7f97cfa28603fcf5d
Closes-Bug: #1521541

oslosphinx/__init__.py

@@ -26,7 +26,8 @@ def _guess_cgit_link():
         git_remote = subprocess.check_output(
             ['git', 'config', '--local', '--get', 'remote.origin.url']
         )
-    except subprocess.CalledProcessError:
+    except (OSError, subprocess.CalledProcessError):
+        # git is not present or the command failed
         return None
     else:
         if six.PY3: