Grubby improvements for use in autotest

[Cleber Rosa <crosa redhat com>]

We have been trying to use Grubby as the booloader entries manager
for autotest. We have found along the way that we could use some
extra features, and here are a couple of them. Expect more to
follow. Sending early hoping to get feedback.

Series summary:

[PATCH 1/5] Makefile: do not link against glib-2.0
[PATCH 2/5] GRUB: Fix detection by increasing offset when comparing
[PATCH 3/5] test.sh: add feature for testing the output of a grubby
[PATCH 4/5] Add new '--default-index' feature.
[PATCH 5/5] Add new '--default-title' feature.