Improve thread safety of SwaggerClient

SwaggerClient discovers methods by reading a swagger document, creating
instances of _ClientMethodFactory for paths in the swagger, and
assigning those instances as class attributes of SwaggerClient.

This means that a single instance of each _ClientMethodFactory is shared
across threads. This is not so good because _ClientMethodFactories
store state associated with requests. In particular, consider the
following scenario:

Thread-1: client = hca.dss.DSSClient()
Thread-2: client = hca.dss.DSSClient()
Thread-1: with client.get_file.stream(...) as handle:
Thread-2: with client.get_file.stream(...) as handle:
Thread-1: handle.raw.read()

Depending on the execution of __enter__, Thread-1 may have just read from
the file for Thread-2! Going on,

Thread-1: __exit__ the with block
Thread-2: handle.raw.read()
Thread-2: __exit__ the with block
Exception: NoneType has no attribute close()

Or you know, something like that.

This change makes the methods instance attributes.

Author: mckinsel

hca/util/__init__.py

@@ -468,7 +468,7 @@ def _build_client_method(self, http_method, http_path, method_data):
         docstring += "\n\n" + _md2rst(method_data["description"])
         client_method.__doc__ = docstring
 
-        setattr(self.__class__, method_name, types.MethodType(client_method, SwaggerClient))
+        setattr(self, method_name, types.MethodType(client_method, SwaggerClient))
         self.methods[method_name] = dict(method_data, entry_point=getattr(self, method_name)._cli_call,
                                          signature=client_method.__signature__, args=method_args)