librados: clear g_ceph_context on shutdown

Signed-off-by: Casey Bodley <casey@linuxbox.com>
memstore: decode fields from OP_SETALLOCHINT

despite being a noop, it still needs to decode its arguments to prevent
trashing the next operation in the transaction.

this case is exercised by rbd workloads, and results in an assertion

Signed-off-by: Casey Bodley <casey@linuxbox.com>
config: -x, --xio as alias for cluster_rdma

Signed-off-by: Casey Bodley <casey@linuxbox.com>
rados: removed xio_connect() from interface

the rados client now uses conf.client_rdma to decide between tcp and
rdma messengers.  removed parsing of --xio from the rbd and rados tools,
which are now handled as global aliases for client_rdma

Signed-off-by: Casey Bodley <casey@linuxbox.com>