Bug 711679 - unresponsive LDAP service when deleting vlv on replica
https://bugzilla.redhat.com/show_bug.cgi?id=711679
Description: Normal operation acquires rlock on be_lock, then locks
inst_config_mutex. Function instance_set_busy_and_readonly used to
lock them in the opposite order, which caused the server deadlock.
This patch fixes it by releasing inst_config_mutex before acquiring
wlock on be_lock in slapi_mtn_be_set_readonly.
(cherry picked from commit b554264e6b6056414d17044991c3b5ec839d0981)