Add --prefer-source and --no-interaction

Add additional flags to the composer install to avoid hitting
the rate limiting that is applied by GitHub and results in
intermittent build failures.
Merge pull request #31 from MageTest/hotfix/travis-github-ratelimit

Add --prefer-source and --no-interaction
Merge pull request #30 from MageTest/feature/refactor

Feature/refactor
Merge pull request #32 from MageTest/feature/refactor

Feature/refactor
Prophecy repository needs to be temporarily loaded from git
Termporarily redirected to a different vendor name
Extension should bootstrap Magento
Prophecy and PhpSpec repository needs to be temporarily loaded from
a forked git repo
Enabled interactive mode for debugging purposes
Non debugging mode has to be enabled back
Composer has to be always up to date
Merge pull request #33 from MageTest/feature/refactor

Continuos refactoring
Fixed conflict generated by github merge