Refactor: libcrmcommon: Log messages coming from certain domains.

Instead of overriding the global default handler with our own, we can
tell glib to use it only for G_LOG_DOMAIN. Additionally, log messages
coming from the glib domains so that any assertions caused by
pacemaker's usage of glib will use our handler as well. All other
domains will continue to use the glib default.

This means that linking with libpacemaker will not override third party
program logging. It also allows those programs to override our "GLib"
domain logging with their own.

Additionally, we should mark all log messages coming from the Pacemaker
domain as being non-fatal. Other domains can do whatever they want and
we won't override it.

Fixes T837