hardware_RamFio: Add default SELinux context when mounting ramfs

This test fails when SELinux is enabled, as ramfs default context
is u:object_r:unlabeled:s0,

tmpfs uses a default u:object_r:tmpfs:s0 context, that allows
normal users to write to the directory, let's use that as well.

BUG=chromium:605309
TEST=test_that host.xyz hardware_RamFio

Change-Id: I6561750bfd4790129536f841b480bfdf74c649a5
Reviewed-on: https://chromium-review.googlesource.com/340092
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Junichi Uekawa <uekawa@chromium.org>
diff --git a/client/site_tests/hardware_RamFio/hardware_RamFio.py b/client/site_tests/hardware_RamFio/hardware_RamFio.py
index 9807df8..9b2f404 100644
--- a/client/site_tests/hardware_RamFio/hardware_RamFio.py
+++ b/client/site_tests/hardware_RamFio/hardware_RamFio.py
@@ -39,7 +39,7 @@
             return
 
         utils.run('mkdir -p /tmp/ramdisk')
-        utils.run('mount -t ramfs ramfs /tmp/ramdisk')
+        utils.run('mount -t ramfs -o context=u:object_r:tmpfs:s0 ramfs /tmp/ramdisk')
 
         self.job.run_test('hardware_StorageFio',
                           dev='/tmp/ramdisk/test_file',