Add retry mechanism to handle write failures of fog

[simmhan]

The current implementation finds the replica locations and these locations are then written to by the client. The order we took is : first write the local replica then write the remote ones. However in case if there are fog failures, then the write may not succeed and retry is needed to achieve the expected reliability.

Talk to parent fog to get alternative in case fog failure?
Related to general concept of handling fog failures/buddy failures, #22