Support unpacking train options from URI query values

[lamont-granquist]

Pretty simple to support arbitrary options in URIs so that stuff like ssh://user:pass@host.com:123/path?bastion_host=stronghold.example.org&bastion_user=bulwark becomes valid. This came up as a result of the work in chef/ohai#1503 to support ohai over train and to allow passing a URL into ohai with the --target option on the command line such that it doesn't require the presence of a .chef/crendentials file.

[chef-expeditor]

Hello lamont-granquist! Thanks for the pull request!

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[lamont-granquist]

paging @clintoncwolfe and @Schwad for review