(FM-2010) Tomcat download mirrors are flaky (tests)

This refactors out download urls in the test manifests and parametrizes
them within the spec_helper_acceptance.rb to allow using internal
resources (default if ran in CI)
Merge pull request #67 from justinstoller/maint/master/FM-2010_use_internal_mirrors

(FM-2010) Tomcat download mirrors are flaky (tests)