Set simulator environment provided by CoreSimulator when running logic tests.

In Xcode 6 `sim` doesn't set `CFFIXED_USER_HOME` if simulator is not launched but this environment is used, for example, by NSHomeDirectory().
To avoid similar situations in future let's set all simulator environments provided by CoreSimulator framework before running logic tests.
Merge pull request #410 from facebook/nekto/set_sim_envs

Set simulator environment provided by CoreSimulator when running logic tests.