add support for "sensitive" provider fields which will be stored
in memory for the lifetime of a cluster operation and then purged.
Also changing all cluster operation requests to be able to take
in a "providerFields" map to pass in these fields as needed. Any
provider field that is sensitive and required must be passed in
the request for each cluster operation.
various checkstyle fixes and rebase problem fixes.
keep sensitive fields for the lifetime of a cluster.
Throw an exception if we were unable to write to memcache.
no state between tests.
Merge pull request #442 from continuuity/feature/add-credential-store

Feature/add credential store