Prevent storage manager creation during validate.

Delay the instantiation of an agent object until it is actually needed.
Instantiating an agent object creates an entry in the storage_managers table,
this is not the desired behavior when validating the storage manager's credentials.

https://bugzilla.redhat.com/show_bug.cgi?id=1123955
Merge pull request #440 from roliveri/ontap_client

Prevent storage manager creation during validate.