consolekit: dep on polkit and glib-2.0-native

It appears the polkit support is optional, but currently there's no way to 
disable it, so we must depend on it to ensure deterministic builds. 
glib-2.0-native is required for glib-gettextize.

JIRA: SB-1507

Signed-off-by: Christopher Larson <kergoth@gmail.com>