Adding a RestClient testcase
Bunch of cleanup changes:
* Better shutdown of Rest server
* Fixed bug in Get, GetAll parsing in R2Store
* Added GetVersions in R2Store
* Modified key encoding to use encodeBase64URLSafeString
  instead of standard base64 encoding
* Additional tests for R2Store and RestClient
Modified RestServiceR2StoreTest to use Rest server port
Catching Bootstrap exception while starting CoordinatorService. This is done to ensure Coordinator comes up even without a valid cluster