support/run-tests: check for empty sequences in a pythonic way

According to PEP8 empty sequences should be checked as booleans.

Fixes the following PEP8 warning:
Do not use `len(SEQUENCE)` to determine if a sequence is empty

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/testing/run-tests

@@ -70,7 +70,7 @@ def main():
 
     BRConfigTest.outputdir = os.path.abspath(args.output)
 
-    if args.all is False and len(args.testname) == 0:
+    if args.all is False and not args.testname:
         print("No test selected")
         print("")
         parser.print_help()
@@ -112,7 +112,7 @@ def main():
                   "-s", test_dir,
                   "-c", os.path.join(test_dir, "conf/unittest.cfg")]
 
-    if len(args.testname) != 0:
+    if args.testname:
         nose2_args += args.testname
 
     nose2.discover(argv=nose2_args)