Use SafeYAML.load to avoid YAML monkeypatch in safe_yaml.

This will leave YAML loading in Test Kitchen as implementation detail
and avoid polluting other Ruby objects.
Ensure that `kitchen help` exits non-zero on failure.

This should be default Thor behavior, but we can control it in any case.

Closes #305
Add local & global file locations with environment variables.

Previous to this commit you could override the location of your
`.kitchen.yml` with the `KITCHEN_YAML` environment variable. For
example:

    KITCHEN_YAML=Kitchen.yaml kitchen list

Now the local and global config file locations can also be overridden
with the following environment variables:

* `KITCHEN_LOCAL_YAML`
* `KITCHEN_GLOBAL_YAML`

The local override might be useful in a hosted CI environment where your
configuration overrides need to be added into your project repository.
You could therefore setup an environment variable such as:

    KITCHEN_LOCAL_YAML=.kitchen.ci.yml

That wouldn't be used in day-to-day local development.

Thanks to @coderanger and @damm for the idea and use case.

Closes #304
Merge pull request #306 from test-kitchen/kitchen-local-yaml-envvar

Add local & global file locations with environment variables.
Merge pull request #303 from fnichol/safe-yaml-lib

Use SafeYAML.load to avoid YAML monkeypatch in safe_yaml.
Bump safe_yaml version dependency to ~> 1.0.
adding /opt/local/bin to search path. smartmachines need this otherwise curl cant find certificates
Fix Windows path matching issues introduced by 1c924af2e9
Allow files in subdirectories in "helpers" directory

Closes #312
Upload chef clients data
Add reference to IRC transcripts in README.
Merge pull request #309 from someara/smartos-curl

adding /opt/local/bin to search path. smartmachines need this otherwise ...
Add TravisCI testing for Ruby 2.1.0.
Merge pull request #310 from rarenerd/fix_yaml_tests

Fix Windows path matching issues introduced by 1c924af2e9
Merge pull request #313 from mthssdrbrg/helpers-directories

Allow files in subdirectories in "helpers" directory
[CLI] Add test for exact match over regex at start of token.

Closes #316
Merge pull request #318 from jtimberman/jtimberman/chef-clients-upload

Upload chef clients data
Stub in a dummy bootstrap if none are found in shell provisioner.

References #335
Kamalika | added exit status check in chef-zero support for chef 10
Pin minitest to ~> 5.1.0 for moment.