rbd: Simplify opening RADOS IoCTX

Reduces code and brings logging back to one function.
rbd: Log return status when creating image fails

This makes it easier to track back to a failure inside librbd
or librados based on the return status.
rbd: Set timeout options for librados

These timeout values make librados/librbd return -ETIMEDOUT when a
operation is blocking due to a failing/unreachable Ceph cluster.

By having the operations time out libvirt will not block.