ONTAP: cache templates on primary storage and clone volumes from them

[rajiv-jain-netapp]

Enable the managed-storage template cache flow for the ONTAP primary storage plugin so that VM root volumes are cloned from a template copy kept on the pool's FlexVolume instead of being copied from secondary storage for every deployment.

• Advertise CAN_CREATE_VOLUME_FROM_VOLUME from the datastore driver.
• Create the template cache on primary: an iSCSI LUN (identity tracked on template_spool_ref) or a qcow2 file for NFS, populated by the KVM host.
• Clone new volumes from the cached template: LUN clone for iSCSI and ONTAP file clone (FileCloneRequest) for NFS, growing the clone when the disk offering is larger than the template.
• Clean up the cached LUN/file when the template is removed from the pool; a missing file is treated as already deleted.
• Move protocol-specific create/clone/resize logic into UnifiedSANStrategy and UnifiedNASStrategy, and add a StorageStrategy helper to poll an optional async job.
• Add unit tests for the driver and the NAS/SAN strategies.

Description

This PR...

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)
• Build/CI
• Test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Bug Severity

• BLOCKER
• Critical
• Major
• Minor
• Trivial

Screenshots (if appropriate):

How Has This Been Tested?

1. Junit tests are incorporated.
2. Additional we tested by running the feature for
   1. create VM for the first time for a given template and storage-pool, workflow created a template and VM subsequently
   2. On create of another VM in sequence with the same template and storage-pool, we are finding VM instance created is pretty fast since it used local template cache.
   3. We tested the workflows for both iSCSI and NFS3 protocol.

[rajiv-jain-netapp]

@blueorangutan package

[rajiv-jain-netapp]

@DaanHoogland @nvazquez @weizhouapache FYI