lint: Add --only agr to run only the specified linters.

tools/lint

@@ -135,7 +135,7 @@ def run():
         failed = check_pep8(list(python_part2))
         return 1 if failed else 0
 
-    linter_config.do_lint()
+    linter_config.do_lint(only=args.only)
 
 if __name__ == '__main__':
     run()

tools/zulint/command.py

@@ -30,6 +30,10 @@ def add_default_linter_arguments(parser):
                         default=[],
                         type=split_arg_into_list,
                         help='Specify linters to skip, eg: --skip=mypy,gitlint')
+    parser.add_argument('--only',
+                        default=[],
+                        type=split_arg_into_list,
+                        help='Specify linters to run, eg: --only=mypy,gitlint')
 
 def split_arg_into_list(arg):
     # type: (str) -> List[str]
@@ -107,7 +111,10 @@ class LinterConfig:
 
         self.lint_functions[name] = run_linter
 
-    def do_lint(self):
-        # type: () -> None
+    def do_lint(self, only=[]):
+        # type: (List[str]) -> None
+        if only:
+            self.lint_functions = {linter: self.lint_functions[linter] for linter in only}
+
         failed = run_parallel(self.lint_functions)
         sys.exit(1 if failed else 0)