selftests/mount: output WARN messages when mount test skipped

If /proc/self/uid_map doesn't exist, mount test case exits
wthout any warning. Fix it to print a warning that the test
is skipped because /proc/self/uid_map doesn't exist.
Signed-off-by: NZhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/mount/Makefile

@@ -9,7 +9,12 @@ unprivileged-remount-test: unprivileged-remount-test.c
 include ../lib.mk
 
 TEST_PROGS := unprivileged-remount-test
-override RUN_TESTS := if [ -f /proc/self/uid_map ] ; then ./unprivileged-remount-test ; fi
+override RUN_TESTS := if [ -f /proc/self/uid_map ] ; \
+		      then	\
+				./unprivileged-remount-test ; \
+		      else	\
+				echo "WARN: No /proc/self/uid_map exist, test skipped." ; \
+		      fi
 override EMIT_TESTS := echo "$(RUN_TESTS)"
 
 clean: