Add support for --skip-tags argument

This allows for skipping tasks which match the provided tags, using
the ansible-playbook argument of the same name.

This can be useful in combination with --tags, to skip reconfiguration
of the common tasks:

kolla-ansible reconfigure --tags nova --skip-tags common

Change-Id: I766552f7ae4099da3d174759f4a609ffe8b4d89f