add integration_name kwarg to the API constructors.

You can use the integration_name argument to track API usage for a specific script or integration in the server access.log. For example:

```
In [2]: c=CbEnterpriseResponseAPI(integration_name="Splunk-App")
```

Will generate the following in the Cb server's access log:

```
`::ffff:1.2.3.4 - - [17/Oct/2016:19:47:10 -0400(0.004)] "GET /api/info HTTP/1.1" 200 297 "-" "cbapi/0.9.8 Python/2.7.10 Splunk-App" "-"
```

src/cbapi/connection.py

@@ -166,6 +166,7 @@ class BaseAPI(object):
     def __init__(self, *args, **kwargs):
         product_name = kwargs.pop("product_name", None)
         credential_file = kwargs.pop("credential_file", None)
+        integration_name = kwargs.pop("integration_name", None)
 
         self.credential_store = CredentialStore(product_name, credential_file=credential_file)
 
@@ -182,7 +183,7 @@ def __init__(self, *args, **kwargs):
             self.credential_profile_name = kwargs.pop("profile", None)
             self.credentials = self.credential_store.get_credentials(self.credential_profile_name)
 
-        self.session = Connection(self.credentials)
+        self.session = Connection(self.credentials, integration_name=integration_name)
 
     def raise_unless_json(self, ret, expected):
         if ret.status_code == 200: