[develop] Fix Mac builds on Travis

[scottarnette]

Change Description

Added various improvements to Mac builds on TravisCI:

• Ensured that -DBUILD_MONGO_DB_PLUGIN=true is not set on Mac builds in TravisCI.
  • This resulted in every Mac build that occurred in Travis to fail due to timeouts in the mongo serial test.
• Updated brew packages for Mac builds on TravisCI.
  • Brew packages listed on .travis.yml were out of date compared to .cicd/platforms/macos-10.14.sh.
• Add echos for cmake and make commands executed on all Mac builds.
  • Linux builds had echo statements that displayed all steps executed within Docker. This will help to ensure what cmake and make commands were executed during debug situations.

See:
https://travis-ci.com/EOSIO/eos/jobs/237611319 | TravisCI Mac build.

Consensus Changes

• Consensus Changes

API Changes

• API Changes

Documentation Additions

• Documentation Additions