Add stub_env dependency to help test ENV variables
Add stub_env to rspec config
Remove before/after device target hooks in launcher spec
Replace set_device_target with stub_env
Remove unnecessary spec in launcher

Case was already covered in another spec.
Replace ENV['DEVICE_TARGET'] in launcher spec w/ stub_env
Stub 'DETECT_CONNECTED_DEVICE' in launcher spec
Remove DEVICE_TARGET from before/after integration core spec
Use stub_env device target in integration/launcher spec
Use stub_env to DEVICE_TARGET in reset app sandbox spec
Merge pull request #601 from calabash/feature/fix-flickering-rspec-tests-DEVICE_TARGET-setting

Fix flickering rspec tests by stubbing the ENV['DEVICE_TARGET'] value