restructure: rm -rf tools, move test requires

To pave the path for the project structure of the future, tools/ is
being eliminated.

New commands/utils should be added as entry points and placed in cmd/

tools/system-test-requires -> system-test-requirements.txt

Change-Id: I14b3189f2b2a1cee6508952a46274e00514addac
Merge "restructure: rm -rf tools, move test requires"