qibuild.get_known_cmake_generators: use qibuild.config.get_build_env
qibuild.get_known_cmake_generators: use qibuild.config.get_build_env

Change-Id: I992392b4d0905ac0d19e0583046100a2e7ee2233

dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild