Add RADOS lock mechanism to the librados C/C++ API.

Add functions to the librados C/C++ API, to take advantage and utilize the
advisory locking system offered by RADOS.

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Filippos Giannakos <philipgian@grnet.gr>
Add RADOS API lock tests

Add tests for the advisory locking API calls.

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Filippos Giannakos <philipgian@grnet.gr>
ceph-test: add ceph_test_rados_api_lock to packaging and qa

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Makefile.am: add -ldl to unittest_pglog

b70868e007ffa56e0eabf22b4ca836327c5f82d4 broke non-package builds on
ubuntu and debian. This fixes the problem, and is required for anything
compiling class_api.cc.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
qa: stop running xfstests 192 in qemu

This test is unreliable in a vm since it relies on command timing for
checking access time.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>