Expand the matrix on the keys xcode_sdk and xcode_scheme
Expand the matrix on the keys xcode_sdk and xcode_scheme

This allows for these variables to be defined as config entries instead
of environment variables.

Tiger66639/travis-core,Tiger66639/travis-core,travis-ci/travis-core,final-ci/travis-core,GistIcon/travis-core,developerfm/travis-core,kidaa/travis-core,jantman/travis-core,kidaa/travis-core,Tiger66639/travis-core,developerfm/travis-core,final-ci/travis-core,GistIcon/travis-core,kidaa/travis-core,travis-ci/travis-core,final-ci/travis-core,jantman/travis-core,GistIcon/travis-core,developerfm/travis-core,travis-ci/travis-core