selftests: change lib.mk RUN_TESTS to take test list as an argument

Change lib.mk RUN_TESTS to take test list as an argument. This will
allow it to be called from individual test makefiles to run additional
tests that aren't suitable for a default kselftest run. As an example,
timers test includes destructive tests that aren't included in the
common run_tests target.

Change times/Makefile to use RUN_TESTS call with destructive test list
as an argument instead of using its own RUN_TESTS target.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>