totemsrp: Show English message when memb_state_gather_enter is called

The reason why memb_state_gather_enter is invoked was printed
in integer code. This patch introduces human readable English
messages for the code.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>