CP-5352: PR-1634: Request and consume list of SRs required to recover a VM / vApp, and add Resolve All button.

1. Added AugustaOrGreater method to Helpers class (which is preferred method over MethodExists to check if a xapi call is available on a server). Also removed MethodExists method.
2. Utilized AugustaOrGreater method in GetDRMissingSRs method in both VM and VM_appliance classes.