Fix doc generation for python 3

1. The html_last_updated_fmt sphinx setting was providing a byte string
   where sphinx expected a str, which produced  warnings (and therefore
   failures):

     WARNING: The config value `html_last_updated_fmt' has type `bytes', expected to ['str'].

   The solution provided is copied from cinder's solution[1].

2. The .keys() method in python 3 returns a dict_keys object rather than
   a list and it does not include a .sort() method. This patch swaps
   .sort() out for the global function sorted() which works in both python
   2 and python 3.

This came up because on some newer distros that don't install python 2
by default, virtualenv defaults to creating a python 3 environment when
none is specified.

[1] https://review.openstack.org/#/c/433081

Change-Id: I68b796fa2e33fd6c3df67b542def31e6ba620944

api-ref/source/conf.py

@@ -171,8 +171,8 @@ pygments_style = 'sphinx'
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
            "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0]
+    html_last_updated_fmt = subprocess.check_output(
+        git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')

doc/ext/support_matrix.py

@@ -319,8 +319,7 @@ class SupportMatrixDirective(rst.Directive):
         summaryhead.append(header)
 
         # then one column for each hypervisor driver
-        impls = matrix.targets.keys()
-        impls.sort()
+        impls = sorted(matrix.targets.keys())
         for key in impls:
             target = matrix.targets[key]
             implcol = nodes.entry()
@@ -352,8 +351,7 @@ class SupportMatrixDirective(rst.Directive):
                 classes=["sp_feature_" + feature.status]))
 
             # and then one column for each hypervisor driver
-            impls = matrix.targets.keys()
-            impls.sort()
+            impls = sorted(matrix.targets.keys())
             for key in impls:
                 target = matrix.targets[key]
                 impl = feature.implementations[key]

doc/source/conf.py

@@ -167,8 +167,8 @@ html_static_path = ['_static']
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
            "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0]
+    html_last_updated_fmt = subprocess.check_output(
+        git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')