Merge changes from topic "fcm_version"

* changes:
  Add AssembleVintfTest
  assemble_vintf: warn for missing env var for fwk_cm.empty.xml
  Add Named<T> in place of std::pair<std::string, T>
  assemble_vintf: move logic to CompatibilityMatrix::combine
  Use base::Split to replace tokenize() function.
  assemble_vintf: refactor to prepare for test