v0.6.0

Massive release which adds support for the new platforms: RHEL6/CentOS6, RHEL7/CentOS7 and focused on quality and stability.
See: https://stackstorm.com/2017/02/02/introducing-ansible-playbooks-deploy-stackstorm/

• Chg #11: Rename mistral -> st2mistral role (@humblearner)
• Chg #94: Rename mistral_ -> st2mistral_ vars (@armab)
• Chg #76: Remove galaxy AXNS.postgresql in favor of own postgresql role (@humblearner)
• Chg #83: Changed val to install st2 latest st2_version=stable -> st2_version=latest (@armab)
• Chg #84: Renamed var: enable_auth -> st2_auth_enable in st2 role (@armab)

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• New #70: Add EL6/7 support for rabbitmq role (@humblearner)
• New #65: Add EL6/7 support for mongodb role (@humblearner)
• New #72: Add multi-machine support (4 platforms) in Vagrantfile (@humblearner)
• New #78: EL6/7 support for st2mistral role, introduce new postgresql role (@humblearner)
• New #80: Include fake meta in a root dir to support install via ansible-galaxy cli (@armab)
• New #69: Add CentOS6 CI in Travis (@armab)
• New #68: Add CentOS7 CI in Travis (@armab)
• New #52: Add ansible-lint CI checks via CircleCI (@armab)
• New #77: Add EL6/7 support for st2web role, introduce new nginx role (@humblearner)
• New #66: Add EL6/7 support for st2 and st2repos roles, introduce new epel role (@Mierdin)
• Enh #61: Replace outdated sudo with become, minor enhancements (@Mierdin)
• Enh #62: Make Ubuntu Xenial default Vagrantfile box (@Mierdin)
• Enh #73: Ensure rabbitmq is enabled and running (@armab)
• Enh #85: Ensure st2 services are enabled and running (@armab)
• Fix #6: Idempotence (@humblearner, @armab)
• Fix #64: Fix mongodb installation failing at task: Add mongodb key (@humblearner)
• Fix #63: Fix Vagrantfile SSH port collisions on some environments (@humblearner)
• Fix #90: Don't update cache during package installs (@armab)
• Fix #92: Add missing dependencies for nginx role (@humblearner)
• Fix #93: Fix SELinux module work for nginx role (@armab)
• Fix #97: Add missing step to disable requiretty for st2 system user (@Mierdin)
• Fix #98: Fix st2web smoke-test can't access webui in AWS environment (@Mierdin)
• Fix #96: Multiple final fixes and improvements to support EL6/7 (@armab)
• Fix #101: Fix task include in postgresql role (@armab)