Raise AuthException on 401 response

[nick-mccoy]

The tap was not catching 401 responses (Auth Error). This changes the tap so it looks for a 401 and raises an exception when it happens.

[nick-mccoy]

Tested on a problematic connection, and things look good:

$ /home/vagrant/.virtualenvs/tap-github/bin/tap-github --config /tmp/tap_config.json --properties /tmp/properties.json --catalog /tmp/catalog.json --state /tmp/tap_state.json
{"stream": "assignees", "type": "SCHEMA", "key_properties": ["id"], "schema": {"properties": {"url": {"type": ["null", "string"], "inclusion": "available", "selected": true}, "type": {"type": ["null", "string"], "inclusion": "available", "selected": true}, "id": {"type":
["null", "integer"], "inclusion": "automatic", "selected": false}, "login": {"type": ["null", "string"], "inclusion": "available", "selected": true}}, "additionalProperties": false, "selected": true, "type": ["null", "object"]}}
INFO METRIC: {"type": "timer", "value": 0.18870115280151367, "tags": {"endpoint": "assignees", "status": "failed"}, "metric": "http_request_duration"}
INFO METRIC: {"type": "counter", "value": 0, "tags": {"endpoint": "assignees"}, "metric": "record_count"}
CRITICAL {"message":"Bad credentials","documentation_url":"https://developer.github.com/v3"}
Traceback (most recent call last):
  File "/home/vagrant/.virtualenvs/tap-github/bin/tap-github", line 9, in <module>
    load_entry_point('tap-github==1.0.0', 'console_scripts', 'tap-github')()
  File "/home/vagrant/.virtualenvs/tap-github/lib/python3.4/site-packages/singer/utils.py", line 192, in wrapped
    return fnc(*args, **kwargs)
  File "/opt/code/tap-github/tap_github.py", line 390, in main
    do_sync(args.config, args.state, catalog)
  File "/opt/code/tap-github/tap_github.py", line 363, in do_sync
    state = sync_func(stream_schema, config, state, mdata)
  File "/opt/code/tap-github/tap_github.py", line 180, in get_all_assignees
    'https://api.github.com/repos/{}/assignees'.format(repo_path)
  File "/opt/code/tap-github/tap_github.py", line 41, in authed_get_all_pages
    r = authed_get(source, url, headers)
  File "/opt/code/tap-github/tap_github.py", line 34, in authed_get
    raise AuthException(resp.text)
tap_github.AuthException: {"message":"Bad credentials","documentation_url":"https://developer.github.com/v3"}
(tap-github)

[nick-mccoy]

Should address #24 and #25