Feature/provider resources

this PR improves support for uploading of plugin credentials, and passing the necessary info to the plugins.  google provider updates included in this PR, other plugins will follow in separate PRs

changes to provisioner worker:
- [x] sets the current working directory to the plugin's resource work dir, for the duration of the plugin's execution
- [x] bootstrap now relies on ``task['config']['automators']``.  removed the default case of running bootstrap for all known automators, since this should never happen, and the code to handle this case was getting ugly.

changes to the google provider:
- [x] class variables to define the known relative paths for resources (matching those defined in the json)
- [x] constructing the resource path from those, and validating up front.

This cannot happen, since they're both required, anyway.