Import recent rootwrap features in local rootwrap

Import features developed in oslo-rootwrap during the Grizzly cycle (and
recently in havana) into quantum-rootwrap. This is the first step toward
using the common oslo-rootwrap into Quantum: the goal being to make both
implementations converge, we should avoid making local changes (and push
any required change into oslo-rootwrap instead from now on).

New features include:
- Optional logging (use_syslog)
- Searching for executables in a specified binary path (exec_dirs)
- New path-based PathFilter

Those features required a refactoring in the way executables are matched
and in configuration loading.

Implements bp quantum-rootwrap-new-features

Change-Id: Ia6a2e91c297ade471448dae0964adfd001a46086
Merge "Import recent rootwrap features in local rootwrap"