BackupVerificationService and Backup Cache
(#773): BackupVerificationService
(#779): Put a cache for the getObjectExist API call to S3. This will help keep the cost of this call at bay.
(#779): Put a rate limiter for getObjectExist API call to S3 so we can limit the no. of calls.
(#782): Provide an override method to force Priam to replace a particular IP.