ipatests: add test_winsyncmigrate suite to nightly runs
    
    The test suite test_winsyncmigrate was missing in nightly definitions
    because CI was lacking configuration needed for establishing winsync
    agreement: the Certificate Authority needs to be configured on
    Windows AD instance. Now that PR-CI is updated to include said changes, we
    can start executing this test suite. It is not reasonable to add it to
    gating as this suite is time consuming just like other tests requiring
    provisioning of AD instances.
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>