LU-4795 obd: Remove server_{get,put}_mount_2() functions

LU-4795 obd: Remove server_{get,put}_mount_2() functions

This patch fixes server_put_mount() to call server_deregister_mount()
only if the caller is never going to need the mount again. The only
caller of server_get_mount_2(), lustre_find_lwp_by_index(), is
changed to now call server_get_mount() and server_put_mount()
without calling server_deregister_mount().

Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Change-Id: I37fd00bd477f946ac1bd8375da4899c2a1fe9e22
Reviewed-on: http://review.whamcloud.com/9749
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>