added helper function to read the clusterID mapping
from the mounted file.
The clusterID mapping contains below mappings
* ClusterID mappings (to cluster to which we are failingover
and from which cluster failover happened)
* RBD PoolID mapping of between the clusters.
* CephFS FscID mapping between the clusters.
Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
