rgw/datalog: Manage and shutdown tasks properly

rgw/datalog: Manage and shutdown tasks properly

This is slightly ugly but good enough for now. Make sure we can block
when shutting down background tasks.

Remove a few `driver` parameters that are unused. This lets us
simplify the IAM Policy and Lua tests and not construct stores we
never use. (Which is good since we aren't running them under a cluster.)

Signed-off-by: Adam C. Emerson <aemerson@redhat.com>
(cherry picked from commit 3def99eec5df353a0fb34be79d9e98a08eb05985)

Conflicts:
	src/rgw/driver/rados/rgw_service.cc
	src/rgw/rgw_sal.h
	src/rgw/rgw_sal.cc
 - `#ifdef` changes
	src/test/rgw/test_rgw_iam_policy.cc
	src/test/rgw/test_rgw_lua.cc
 - SAL renaming

Signed-off-by: Adam C. Emerson <aemerson@redhat.com>