Replace deprecated library function os.popen() with subprocess

os.popen() is deprecated since python 2.6.
Resolved with use of subprocess module.

Change-Id: Ia7e19f82bedfa43cd8f98d03fb5a0bb0860d0221
Closes-Bug: #1529836

README.rst

@@ -35,8 +35,9 @@ metadata for the project where the docs reside::
 
    # We ask git for the SHA checksum
    # The git SHA checksum is used by "log-a-bug"
-   git_cmd = "/usr/bin/git log | head -n1 | cut -f2 -d' '"
-   gitsha = os.popen(git_cmd).read().strip('\n')
+   git_cmd = ["/usr/bin/git", "rev-parse", "HEAD"]
+   gitsha = subprocess.Popen(
+       git_cmd, stdout=subprocess.PIPE).communicate()[0].strip('\n')
    # tag that reported bugs will be tagged with
    bug_tag = "your-chosen-tag"
    # source tree

doc/source/conf.py

@@ -12,6 +12,7 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
+import subprocess
 import sys
 import os
 
@@ -67,8 +68,9 @@ release = '1.0'
 #   bug_tag: Tag for categorizing the bug. Must be set manually.
 # These variables are passed to the logabug code via html_context.
 giturl = u'http://git.openstack.org/cgit/openstack/openstackdocstheme/tree/doc/source'
-git_cmd = "/usr/bin/git log | head -n1 | cut -f2 -d' '"
-gitsha = os.popen(git_cmd).read().strip('\n')
+git_cmd = ["/usr/bin/git", "rev-parse", "HEAD"]
+gitsha = subprocess.Popen(
+    git_cmd, stdout=subprocess.PIPE).communicate()[0].strip('\n')
 bug_tag = "doc-builds"
 html_context = {"gitsha": gitsha, "bug_tag": bug_tag, "giturl" : giturl}