should run some cucumber tests in ci

## motivation

At the moment, we are supporting 3 ruby versions (1.9.3, 2.1.0, and 2.1.2).  When I am testing a new calabash feature or fix, I have to 'smoke' test against these 3 versions.  Now consider the number of simulators + ruby device combinations that I need to test in order to be confident that a change will not 'break the build'.

Have a look at this pull request: [#399: reset app and sim content and settings](https://github.com/calabash/calabash-ios/pull/399).  

This is a simulator only change.  The test section shows my checklist of for changes that effect only the simulator.  I had to create another pull request in a different project to demonstrate that the changes 'worked' and then I had to change ruby versions 3 times and run the same tests again.  I would like to try to automate at least the ruby-version testing.

This pull request adds `test/cucumber` to the travis-ci builds.  At the moment, the Features are straight from the calabash-ios-example project.  The Scenarios are very simple - just smoke tests - that are run on all 3 versions of ruby and these simulators:

* iPhone 4in   iOS 6.1
* iPhone 4in   iOS 7.1
* iPhone 4in   iOS 7.0 64 bit `*`
* iPhone 3.5in iOS 6.1
* iPhone 3.5in iOS 7.1
* iPad Retina iOS 6.1
* iPad Retina iOS 7.1
* iPad Retina iOS 7.0 64 bit `*`
* iPhone 3.5in iOS 6.1 launched with ios-sim

`*` iOS 7.1 version fails on ci because it pops a security dialog on the host machine; passes locally.

[PR #399](https://github.com/calabash/calabash-ios/pull/399) no longer merges cleanly.  I would like to merge this pull-request, rebase #399 against master, and then add the cucumber tests that I wrote in https://github.com/calabash/calabash-ios-example/pull/5 to test/cucumber/features.  The tests are simple and short.  Once we see that they pass, we can and should delete them.

My goal here is not to replace the exhaustive testing we get from Briar-cal and RiseUp-cal with Features in test/cucumber.  I want the cukes in test/cucumber to finish quickly and be constantly changing; the should only be testing the most recent changes.

## todo 

- [ ] @krukow needs review

## test

Already run. :)