test-runner: resolve --kernel absolute path

This only posed a problem oddly if the kernel binary was in the same
directory as test-runner. Resolving the absolute path with the
argument parser resolves the issue.

tools/runner.py

@@ -173,7 +173,7 @@ class RunnerArgParse(RunnerCoreArgParse):
 				default=None)
 		self.add_argument('--kernel', '-k',
 				metavar='<kernel>',
-				type=str,
+				type=os.path.abspath,
 				help='Path to kernel/uml image',
 				dest='kernel',
 				default=None)