Added SyncPackagesInFailoverDC job
1. Copies packages from package backups container to packages container in
   Failover DC if the package is not already present or if there is a newer revision of the
   package caused by 'Edit Metadata'
2. Deletes packages from packages container in failover DC which are not
   found in the database, i.e, delete from packages in primary DC

Need to use the sourceUri overload on StartCopyFromAsync
by setting up a SharedAccessKey. Otherwise, it won't copy across
datacenters

1. Tested that the job copies packages from package backups container to
   packages container cross account and cross DC
2. Tested that the job deletes packages from packages container in failover
   DC that are not present in the Database
Incorporated PR comments
Merge pull request #14 from NuGet/daravind/SyncDatacenter-2

Added SyncPackagesInFailoverDC job