selftests: timers: Fix run_destructive_tests target to handle skipped tests

selftests: timers: Fix run_destructive_tests target to handle skipped tests

BugLink: http://bugs.launchpad.net/bugs/1717549
commit df9c011c0a23cf1399c01f896cd359d932ab49b5 upstream.

When a test exits with skip exit code of 4, "make run_destructive_tests"
halts testing. Fix run_destructive_tests target to handle error exit codes.

Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>