Add section for negative tests to HACKING.rst

This commit adds a new section to HACKING.rst to outline the
guidelines for adding negative tests to tempest.

Change-Id: Ieb3fc3670bb9229c6791e5c8c0a7ac4fbde03c4d
Script to filter logs for ERRORs based on whitelist

The script will take a directory or url containing log files.
For now all non-whitelisted errors will be dumped to the console but
the script will always return success. Once we are convinced it is reliable
enough we can change it to fail on non-whitelisted errors.

Partially implements blueprint fail-gate-on-log-errors

Change-Id: I30b0eee1055f47aaad7984d886c739ccf5aa6186
Merge "Script to filter logs for ERRORs based on whitelist"
Merge "Add section for negative tests to HACKING.rst"