* Merge prechecks.yml and site.yml playbook
* Create empty precheck.yml into all roles.

Change-Id: I8a138558a26c0a2a66c5fd48ed37be657c99c1dd
Implements: blueprint condition-pre-check

When using both /run and /run/netns in docker container, mount
propagation won't work when delete namespace after the containers are
restarted. This PS makes /run mount as shared.

Closes-Bug: #1616268
Change-Id: Ie16699e1b193b2bf1263d89ea634e89ea69add9e

Useful for upgrade etc., which is preferablly done serially.

Example usage: tools/kolla-ansible deploy OR tools/kolla-ansible upgrade

Closes-Bug: #1576708

DocImpact

Change-Id: I34b2e16f8ce53e472a4682a4738c4ac0f5abf00c

Due some cinder drivers need multipathing support like this one
http://docs.openstack.org/mitaka/config-reference/block-storage/drivers/ibm-storwize-svc-driver.html

This PS will allow to run these additional drivers when using Kolla.

Implements: blueprint multipath-support
Change-Id: Id6cf29f984c92773bbfc2f95daea573a74701648