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: Zhang Zhen <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/mount/Makefile

···
 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: