…e primary end point:

* Added account2 and key2 to specific the alternate storage; this account is always accessed through the secondary endpoint
* Added “use_secondary” to the Azure repository settings; if true, uses the account2/key2 and secondary endpoint; otherwise, use the original account/key and primary endpoint
* Avoid writing to the secondary endpoint during snapshot repository registration
* Fixed the encapsulation of AzureBlobStore class so that it controls whether to pass on the useSecondary flag; this avoids having a mode in AzureStorageServiceImpl as to which client is selected.

…figuration allows an array of

storage accounts and keys; account2 and key2 removed.  Only one active location_mode per account allowed.

…ory means to use the first one in the list

…ation.

…ud-azure into latest-es-1.6