DEVICE_TARGET should be respected if set

The default_args method was not respecting the DEVICE_TARGET env bar
when launching the simulator; it was always setting

args[:device_target] = 'simulator

even when DEVICE_TARGET set to the another simulator.

As a result, on the default 'iPhone 4in iOS 7' was being launched.
should use simulator_target?
spec require a directories in spec/resources
should increase launch timeout

some machines just need a longer time to launch
@svevang
Merge pull request #373 from calabash/feature/should-be-able-to-launch-any-simulator

should be able to launch any simulator