[PLTF-1720] Publish Avvo gems to both Packagecloud and Artifactory

[vicente-ramos]

@nickmarden This PR is special because it start to implement Gemfile.lock resolution. Please check if next steps are according to expectations:

1. As it is a library next dependencies were move from Gemfile to gemspec:
   mocha for general
   test-unit for test
2. Gemfile.lock was already listed in .gitignore (if was not, it would be added)

[nickmarden]

This formatting is not cosmetic. Please use the format you've used elsewhere.

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[nickmarden]

@vicente-ramos This gem repo is different from many of the others that you've been working on because it is a public repo that is published to a public gem server.

I'm not sure if we need to add support for pushing this gem to Packagecloud or Artifactory if we can push it to and pull it from gemcutter.org or some other public repository. Please research and determine if this PR is even needed. In the future you can review whether the repo is public prior to beginning your PLTF-1607 upgrades. We can discuss the ones that are public to decide whether and how to proceed.