Fix tests for testtools 2.8.0 compatibility

From 2.8.0 testtools, testcase.TestSkipped has been removed we are
advice to replace with testcase.TestSkipped with unittest.skipTest

This PR trying to fix tests that are using TestSkipped by replacing it
with unittest.skipTest..

Closes-Bug: #2131281
Change-Id: I3bbdab71ec47f9c6ac99698aa1225239e7226706
Signed-off-by: Abhishek Bongale <abhishekbongale@outlook.com>
1 file changed