Remote updates with ansible-pull

[jasoncorlett]

Changes:

• Paths in ansible/nimbuserver.yml now relative, allows updating with ansible-pull
• New nimbus-server-update script to run ansible-pull easily
• Tweaks to nimbusserver.json so ansible will work with relative paths, and make using a new CentOS iso image easier

To test:

ansible-pull -U git://github.com/jasoncorlett/nimbusserver-ansible -C remote-update ansible/nimbusserver.yml

OR, if the script is installed:

export NIMBUS_UPDATE_URL="git://github.com/jasoncorlett/nimbusserver-ansible"
export NIMBUS_UPDATE_BRANCH="remote-update"
nimbus-server-update