Revert "nova-multi-cell: Skip test_cold_migrate_unshelved_instance"
Revert "nova-multi-cell: Skip test_cold_migrate_unshelved_instance"

This reverts commit c11f4e533676abc676884053544607d263b3ffca.

Test should work since change:
    I0b81282eba8238d8b64a67e38cf9d6392de1f85c

Conflicts:
        devstack/nova-multi-cell-blacklist.txt

NOTE(aarents): the confict is due to change
I95bc22f7d65454cd9e7b54a0e6d9516f2f204978
Disable qos resize tempest test for nova-multi-cell job

Change-Id: Ib953470cf0ccddfec5f253097ddd7f7f0eaf4883

mahak/nova,klmitch/nova,mahak/nova,klmitch/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova,openstack/nova,klmitch/nova