support/testing: factor out run_cmd_on_host

Currently many test cases call subprocess.check_output on their own.
Factor out that code to an infra method so the call get standardized.

This will be handful when switching the test infra to use Python 3.

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/testing/tests/fs/test_ext.py

@@ -1,5 +1,4 @@
 import os
-import subprocess
 
 import infra.basetest
 
@@ -15,10 +14,7 @@ CHECK_FS_TYPE_CMD = "mount | grep '/dev/root on / type {}'"
 
 def dumpe2fs_run(builddir, image):
     cmd = ["host/sbin/dumpe2fs", os.path.join("images", image)]
-    ret = subprocess.check_output(cmd,
-                                  stderr=open(os.devnull, "w"),
-                                  cwd=builddir,
-                                  env={"LANG": "C"})
+    ret = infra.run_cmd_on_host(builddir, cmd)
     return ret.strip().splitlines()