RESTful APIs for data changes log implemented with test cases

Signed-off-by: Babu Shanmugam <anbu@enovance.com>
rgw: metadata lock/unlock implemented with test cases

metadata lock/unlock implemented with test cases
split Post operations to Lock and Unlock operations, and
checking for WRITE permission only for lock and unlock

Signed-off-by: Babu Shanmugam <anbu@enovance.com>

Conflicts:
	src/rgw/rgw_rest_log.cc
	src/rgw/rgw_rest_log.h

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>