core: VdsDynamicDAO.testUpdateIfNeededPerformance

As this test is based on timing, it fails sporadically, thus generating
inappropriate noise during build time. Moreover, this is a performance
test, not a correctness test, and as such should not be part of the
regular test suite.

Change-Id: I4ce745eb4416ffac0ae7162f69e85b55bd003569
Signed-off-by: Allon Mureinik <amureini@redhat.com>