FIX PR #323 Add ruby API for accessing the "keychain" route

## action items 

- [x] @jgallagher request review
- [x] @krukow needs review

fixes up https://github.com/calabash/calabash-ios/pull/323

## related PR

* https://github.com/calabash/calabash-ios-server/pull/39 - includes testing details
* https://github.com/jmoody/briar-ios-example/pull/14 - project with linked Security.framework
* https://github.com/LittleJoySoftware/calabash-ios-example/tree/test/keychain-additions - project w/o linked Security.framework