CTDB: fix OCF_RESKEY_ctdb_recovery_lock validation (bsc#1088692)

ctdb supports '!' prefix syntax to use a helper binary for recovery
lock functionality. This currently fails the reclock path existence
check.
Add helper binary support by stripping the '!' prefix and trailing
helper binary parameters before checking for existence.

Signed-off-by: David Disseldorp <ddiss@suse.de>