tests/acceptance/virtiofs_submounts.py: evaluate string not length

If the vmlinuz variable is set to anything that evaluates to True,
then the respective arguments should be set.  If the variable contains
an empty string, than it will evaluate to False, and the extra
arguments will not be set.

This keeps the same logic, but improves readability a bit.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Beraldo Leal <bleal@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210412044644.55083-3-crosa@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>

tests/acceptance/virtiofs_submounts.py

@@ -251,7 +251,7 @@ def setUp(self):
 
         super(VirtiofsSubmountsTest, self).setUp(pubkey)
 
-        if len(vmlinuz) > 0:
+        if vmlinuz:
             self.vm.add_args('-kernel', vmlinuz,
                              '-append', 'console=ttyS0 root=/dev/sda1')