oeqa/commands: Ensure sync can be found regardless of PATH

Avoid command not found errors shown in selftest logs due to changes to PATH
settings which also risks intermittent problems due to IO load.

(From OE-Core rev: 40bcae01b0be2f293dea9ab42c6b7f8f47827cf5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/commands.py

@@ -188,7 +188,10 @@ def runCmd(command, ignore_status=False, timeout=None, assert_error=True, sync=T
     # call sync around the tests to ensure the IO queue doesn't get too large, taking any IO
     # hit here rather than in bitbake shutdown.
     if sync:
+        p = os.environ['PATH']
+        os.environ['PATH'] = "/usr/bin:/bin:/usr/sbin:/sbin:" + p
         os.system("sync")
+        os.environ['PATH'] = p
 
     result.command = command
     result.status = cmd.status