Ignore terminal task resources in the Master's Framework struct.

Review: https://reviews.apache.org/r/25844
Fixed an executor accounting bug in framework re-registration.

Review: https://reviews.apache.org/r/25843
Fixed an issue with colored output in post-reviews.py.

Review: https://reviews.apache.org/r/25819
Refactored Node class in libprocess.

Moved class Node out of process.cpp and into its own header as a part
of refactoring process.cpp.

Review: https://reviews.apache.org/r/25847
Refactor test environment validations

Review: https://reviews.apache.org/r/25569