CA-220506: Update rbac role for SR.scan API call.
CA-220506: Update rbac role for SR.scan API call.

Allow VM_POWER_ADMIN to perform `SR.scan` in order to allow
Storage XenMotion.
VM_POWER_ADMIN can perform `VDI.create` and other VDI operations
so its safe to perform `SR.scan`.

Signed-off-by: Sharad Yadav <0ab5d8dd51ae0f2f9ed283cbbbb7a94d110e3347@citrix.com>

Frezzle/xen-api,Frezzle/xen-api,thomassa/xen-api,euanh/xen-api,thomassa/xen-api,Frezzle/xen-api,thomassa/xen-api,thomassa/xen-api,euanh/xen-api,srowe/xen-api,euanh/xen-api,Frezzle/xen-api,srowe/xen-api,euanh/xen-api,Frezzle/xen-api,thomassa/xen-api,srowe/xen-api,euanh/xen-api,srowe/xen-api,srowe/xen-api,thomassa/xen-api,euanh/xen-api