Previously the initial call to connect to a RBD cluster via the RADOS
API could hang indefinitely if network or other environmental related
issues were encountered.
When encountered during a call to update_available_resource this can
result in the local n-cpu service reporting as UP while never being able
to break out of a subsequent RPC timeout loop as documented in bug
This change adds a simple timeout configurable to be used when initially
connecting to the cluster [1][2][3]. The default timeout of 5 seconds
being sufficiently small enough to ensure that if encountered the n-cpu
service will be able to be marked as DOWN before a RPC timeout is seen.
[1] http://docs.ceph.com/docs/luminous/rados/api/python/#rados.Rados.connect
[2] http://docs.ceph.com/docs/mimic/rados/api/python/#rados.Rados.connect
[3] http://docs.ceph.com/docs/nautilus/rados/api/python/#rados.Rados.connect
Closes-bug: #1834048
Change-Id: I67f341bf895d6cc5d503da274c089d443295199e