GFS2: Review bug traps in glops.c

Two of the bug traps here could really be warnings. The others are
converted from BUG() to GLOCK_BUG_ON() since we'll most likely
need to know the glock state in order to debug any issues which
arise. As a result of this, __dump_glock has to be renamed and
is no longer static.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>