rbd: Include return statusses from librados/librbd in logging

With this information it's easier for the user to debug what is
going wrong.
rbd: Simplify opening RADOS IoCTX

Reduces code and brings logging back to one function.
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.