gfs2: Add GL_NOPID flag for process-independent glock holders

Add a GL_NOPID flag to indicate that once a glock holder has been acquired, it
won't be associated with the current process anymore.  This is useful for iopen
and flock glocks which are associated with open files, as well as journal glock
holders and similar which are associated with the filesystem.

Once GL_NOPID is used for all applicable glocks (see the next patches),
processes will no longer be falsely reported as holding glocks which they are
not actually holding in the glocks dump file.  Unlike before, when a process is
reported as having "(ended)", this will indicate an actual bug.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>