Add manage / unmanage support to NetApp cDOT driver

This blueprint describes adding support to the cDOT driver for the driver methods manage_existing and unmanage. The logic follows three sections:

1. Locate the resource to be managed, which is specified as the cDOT flexvol name in the export_path argument.
2. Ensure the flexvol to be brought under Manila management is of the appropriate type, the extra specs from the share type are valid and match the specified pool, and the flexvol has no LUNs or other flexvols mounted underneath it.
3. Rename the flexvol using normal Manila naming conventions, remount it on a new path matching the new name, update it to conform to all relevant qualified extra specs, and remove any existing export rules.