shill: Implement CreateProfile, PushProfile, PopProfile

Collateral fixes: Profiles now create a header at the beginning
of the file, and this feature is plumbed down through key_file_store
and glib.  InitStorage can be configured to fail if the profile
already exists/doesn't yet exist.

BUG=chromium-os:22221
TEST=New unit tests

Change-Id: Ie7c2d0dee97891b7850cec75b74052fce77eee8f
Reviewed-on: https://gerrit.chromium.org/gerrit/10884
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/glib.h b/glib.h
index 9bec9c0..ee30cc9 100644
--- a/glib.h
+++ b/glib.h
@@ -90,6 +90,12 @@
                                  const gchar *group_name,
                                  const gchar *key,
                                  gboolean value);
+  // g_key_file_set_comment
+  virtual gboolean KeyFileSetComment(GKeyFile *key_file,
+                                     const gchar *group_name,
+                                     const gchar *key,
+                                     const gchar *comment,
+                                     GError **error);
   // g_key_file_set_integer
   virtual void KeyFileSetInteger(GKeyFile *key_file,
                                  const gchar *group_name,