Dcos-shakedown

Features:

- `--fail` now defaults to `never`
- the `run_command` and associated agent/master methods now return
both the exit status and captured output

Fixes:

- `kill_process_on_host` method now working, better output
- improved `--stdout-inline` readability
- fixed bug where output from teardown methods did not display if
module only had a single test

Features:

- `--username`, `--password`, and `--oauth-token` can now be
specified via the command line
- updated documentation on installing via PyPI or with virtualenv

Fixes:

- authentication methods (OAuth, user/pass) are only attempted
when the related options are defined
- removed `pytest_runtest_makereport` method which was unused and
causing pytest warning messages on every run

Fixes:

- cluster authentication attempts are sequenced (existing ACS token ->
OAuth token -> username/password combo)
- output from module setup and teardown is now printed to stdout
- multiple test files (or multiple tests) can be again be specified
(broken in `1.1.4`)

Features:

- allow a session to be authenticated using a supplied OAuth token
in `.shakedown` (`oauth_token = <token>`)
- new `delete_agent_log` method to delete logs on agents
- pytest-style single-test specification (`test_file.py::test_name`)

Fixes:

- `dcos-shakedown` command now functions correctly from cmd

Features:

- bumped `dcoscli` version to `0.4.13`
- modified CLI 'short' flags to match SSH/curl

Fixes:

- removed superfluous `key not found` error message when SSH
key could not be located

Features:

- new `--pytest-option` flag to pass CLI options on to pytest
- short (single-character) flags for commonly-used CLI options

Fixes:

- improved `--help` CLI output