subcmds: force consistent help text format

We're inconsistent with help text as to whether it uses title case and
whether it ends in a period.  Add a test to enforce a standard, and use
the style that Python optparse & argparse use themselves (e.g. with the
--help option): always lowercase, and never trailing period.

Change-Id: Ic1defae23daeac0ac9116aaf487427f50b34050d
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/305144
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

subcmds/info.py

@@ -48,7 +48,7 @@ class Info(PagedCommand):
                  help=optparse.SUPPRESS_HELP)
     p.add_option('-l', '--local-only',
                  dest="local", action="store_true",
-                 help="Disable all remote operations")
+                 help="disable all remote operations")
 
   def Execute(self, opt, args):
     self.out = _Coloring(self.client.globalConfig)