ocfs2: Move the hb_ctl_path sysctl into the stack glue.

ocfs2 needs to call out to the hb_ctl program at unmount for all cluster
stacks.  The first step is to move the hb_ctl_path sysctl out of the
o2cb code and into the generic stack glue.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>