link libtotem_pg to libqb

The libtotem_pg library uses symbols from libqb, so it should be
explicitely linked with it. This doesn't cause problems for corosync
binary itself, as it is linked to both libraries, but can cause
problems if anything else links to libtotem_pg.so and automated
checkers can show this as a library problem.

Signed-off-by: Jacek Konieczny <jajcus@jajcus.net>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>