selftests/timers: Use shared logic to run and install tests

Change the timers Makefile to make use of shared run and install logic
in lib.mk. Destructive tests are installed but not run by default.

Add a new variable, TEST_PROGS_EXTENDED, which is a list of extra
programs to install, but which are not run by the default run_tests
logic.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>