oeqa/postactions: Do not use -l option with df

-l option is specific to df provided by coreutils, if df
applet from busybox is used then it does not work and fails
like below

Fixes
   df: invalid option -- 'l'
   BusyBox v1.36.1 () multi-call binary.

   Usage: df [-PkmhT] [-t TYPE] [FILESYSTEM]...
   DEBUG: [Command returned '1' after 0.71 seconds]
   DEBUG: Command: df -hl
   Status: 1 Output:  df: invalid option -- 'l'

it seems worth a compromise to show remote mounted filesystems if any
during ptests and it works with both df implementations

(From OE-Core rev: 75cc1ea4348a2294fdc5ab20530fcff27056ff06)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/postactions.py

@@ -25,7 +25,7 @@ def create_artifacts_directory(d, tc):
 def get_target_disk_usage(d, tc):
     output_file = os.path.join(get_json_result_dir(d), "artifacts", "target_disk_usage.txt")
     try:
-        (status, output) = tc.target.run('df -hl')
+        (status, output) = tc.target.run('df -h')
         with open(output_file, 'w') as f:
             f.write(output)
             f.write("\n")