Source modules.env from apply-test.sh

This causes apply-test.sh to get the list of puppet modules to do
integration test with from modules.env. Modules.env has been
refactored to have three lists of modules: Package modules(MODULES),
SOURCE_MODULES, and INTEGRATION_MODULES.

When PUPPET_INTEGRATION_TEST is not set, INTEGRATION_MODULES is
folded into SOURCE_MODULES.

In apply-test.sh, INTEGRATION_MODULES is sourced from modules.env
and some string/array manipulation is performed to pass each entry
to zuul-cloner.

Change-Id: I47302c5c7e8c41b985f16a05c4e9b8078ea867a3
Merge "Source modules.env from apply-test.sh"