Exclude boto from tests due to broken Liskov Substitution Principle

Starting with python/mypy#2521 mypy is performing stricter function signature
checks.

This makes the stubs diverge from the actual implementation but makes the stubs
internally consistent.  Since this is an actual typing issue in the base
implementation, we need to defer to the original authors to fix it.

Sadly, in this case the breakage is rather fundamental and unlikely to get
fixed by upstream. Consider:

```
  class AWSAuthConnection(object):
    def make_request(self, method, path, headers=None, data='', host=None,
      auth_path=None, sender=None, override_num_retries=None,
      params=None, retry_handler=None): ...

  class AWSQueryConnection(AWSAuthConnection):
    def make_request(self, action, params=None, path='/', verb='GET'): ...
```

Hence, until we have a workaround for the error produced by Mypy, we're
excluding those stubs from being tested against.

tests/mypy_blacklist.txt

@@ -0,0 +1 @@
+third_party/2and3/boto/.*

third_party/2and3/boto/connection.pyi

@@ -111,7 +111,7 @@ class AWSQueryConnection(AWSAuthConnection):
     ResponseError = ...  # type: Any
     def __init__(self, aws_access_key_id: Optional[Any] = ..., aws_secret_access_key: Optional[Any] = ..., is_secure: bool = ..., port: Optional[Any] = ..., proxy: Optional[Any] = ..., proxy_port: Optional[Any] = ..., proxy_user: Optional[Any] = ..., proxy_pass: Optional[Any] = ..., host: Optional[Any] = ..., debug: int = ..., https_connection_factory: Optional[Any] = ..., path: str = ..., security_token: Optional[Any] = ..., validate_certs: bool = ..., profile_name: Optional[Any] = ..., provider: str = ...) -> None: ...
     def get_utf8_value(self, value): ...
-    def make_request(self, action, params: Optional[Any] = ..., path: str = ..., verb: str = ..., *args, **kwargs): ...
+    def make_request(self, action, params: Optional[Any] = ..., path: str = ..., verb: str = ..., *args, **kwargs): ...  # FIXME: signature incompatible with base class
     def build_list_params(self, params, items, label): ...
     def build_complex_list_params(self, params, items, label, names): ...
     def get_list(self, action, params, markers, path: str = ..., parent: Optional[Any] = ..., verb: str = ...): ...

third_party/2and3/boto/s3/connection.pyi

@@ -4,7 +4,7 @@
 
 from .bucket import Bucket
 
-from typing import Any, Optional, Text, Type
+from typing import Any, Dict, Optional, Text, Type
 from boto.connection import AWSAuthConnection
 from boto.exception import BotoClientError
 
@@ -68,4 +68,4 @@ class S3Connection(AWSAuthConnection):
     def lookup(self, bucket_name, validate: bool = ..., headers: Optional[Dict[Text, Text]] = ...): ...
     def create_bucket(self, bucket_name, headers: Optional[Dict[Text, Text]] = ..., location: Any = ..., policy: Optional[Any] = ...): ...
     def delete_bucket(self, bucket, headers: Optional[Dict[Text, Text]] = ...): ...
-    def make_request(self, method, bucket: str = ..., key: str = ..., headers: Optional[Any] = ..., data: str = ..., query_args: Optional[Any] = ..., sender: Optional[Any] = ..., override_num_retries: Optional[Any] = ..., retry_handler: Optional[Any] = ..., *args, **kwargs): ...
+    def make_request(self, method, bucket: str = ..., key: str = ..., headers: Optional[Any] = ..., data: str = ..., query_args: Optional[Any] = ..., sender: Optional[Any] = ..., override_num_retries: Optional[Any] = ..., retry_handler: Optional[Any] = ..., *args, **kwargs): ...  # FIXME: signature incompatible with base class