Enable running tools/run-mypy on a subdirectory.

Previously tools/run-mypy could not run on a subdirectory properly
because run-mypy assumed exclude files to be in that subdirectory.

tools/run-mypy

@@ -10,7 +10,7 @@ import argparse
 import subprocess
 import six
 
-exclude="""
+exclude = """
 api/integrations/
 bots/jabber_mirror_backend.py
 bots/zephyr_mirror_backend.py
@@ -36,6 +36,9 @@ args = parser.parse_args()
 if args.all:
     exclude = []
 
+# find all non-excluded files in current directory
+BASE_DIR = dirname(dirname(abspath(__file__)))
+exclude = [os.path.join(BASE_DIR, fpath) for fpath in exclude]
 python_files = lister.list_files(targets=args.targets, ftypes=['py'], use_shebang=False,
                                  modified_only=args.modified, exclude=exclude)
 
@@ -48,6 +51,7 @@ if six.PY2 and os.path.exists(MYPY_VENV_PATH):
 else:
     mypy_command = "mypy"
 
+# run mypy
 if python_files:
     rc = subprocess.call([mypy_command, "--fast-parser", "--silent-imports", "--py2", "--check-untyped-defs"] + python_files)
     sys.exit(rc)