TestLib: align the colons so the "actual" and "expected" align too

Before:
FAIL!  tst_testcase::testcase: Compared values are not the same
   Actual   (actual): F0O
   Expected (expected): FOO

Now:
FAIL!  tst_testcase::testcase: Compared values are not the same
   Actual   (actual)  : F0O
   Expected (expected): FOO

Change-Id: I6f0768e4ef53e065b85a56879cecbad06fa34aef
Reviewed-by: Jason McDonald <macadder1@gmail.com>