selftests: add quicktest support

Add quicktest support to enable users to choose to run
tests that complete in a short time. Choosing this option
excludes tests that take longer time complete e.g: timers.
User can specify quicktest option from kernel top level or
selftests directory.

Kernel top level directory:
make quicktest=1 kselftest

tools/testing/selftests directory:
make quicktest=1 run_tests
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/Makefile

@@ -16,11 +16,15 @@ TARGETS += ptrace
 TARGETS += seccomp
 TARGETS += size
 TARGETS += sysctl
+ifneq (1, $(quicktest))
 TARGETS += timers
+endif
 TARGETS += user
 TARGETS += vm
 TARGETS += x86
 #Please keep the TARGETS list alphabetically sorted
+# Run "make quicktest=1 run_tests" or
+# "make quicktest=1 kselftest from top level Makefile
 
 TARGETS_HOTPLUG = cpu-hotplug
 TARGETS_HOTPLUG += memory-hotplug