[Migration] Enable SAN based guest to adopt migration test cases to leverage

[balamuruhans]

Currently all the migration scenarios are using NFS shared storage to configure and perform migration, but ideally guest would be based on disk from LUN storage shared across mutiple host. Working on it to bring up the guest with LUN through Avocado-VT and sent a recent PR - avocado-framework/avocado-vt#1593.

Planned to make use of the existing testcases to make use of this guest to perform migration and we need few more code changes in,

• tp-libvirt to avoid guest xml changes currently being done for NFS migration.
• avocado-vt to avoid some migration pre-setups that are not required for SAN migration
  by this changes it is expected to run migration testcases seamlessly on NFS or in SAN based on the configuration params.

[dzhengfy]

This is a good point. But as it is new case, I suggest the new python module be used, and both migrate_vm.py and virsh_migrate.py should be excluded at least, because they already have too many lines.

[balamuruhans]

@dzhengfy I am trying to make most of the changes from framework, so that both migrate_vm.py and virsh_migrate.py would work as is based on the param storage_type = "nfs" for NFS migration and storage_type = "lun" for SAN migration