b-test: add test filtering capability

Add a new argument which allows limiting the test cases to a list
matching the specified regexp. The filter affects all commands except
clean.
Change test case processing to allow specifying a list of tests.

Change-Id: I1ba40798adbcbd902794b477da35eb35f2d728ca
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
2 files changed