Missed doc for section nodes in config file

[Mikhail Zhnichkov]

For section nodes in config we can specify node[1-9], but can not
node[2-12], because it is a wrong regex expression. We should use
node([2-9]|1[0-2]) and its should be documented

[Sergey Reshetnyak (sreshetniak)]

node[2-12] is not valid regexp

[Kirill Bespalov (k-besplv)]

> We should use
> node([2-9]|1[0-2])

Also must be documented that a user always must specify the "end-of-line" in reg-exp like:

 node1$:
   roles: [a,b,c]

otherwise will be matched node10, node11, etc

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/427063

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/427063
Committed: https://git.openstack.org/cgit/openstack/fuel-ccp/commit/?id=b0bae382d70a87cba6385627d53ecb24f0d188ab
Submitter: Jenkins
Branch: master

commit b0bae382d70a87cba6385627d53ecb24f0d188ab
Author: Mikhail <email address hidden>
Date: Tue Jan 31 12:54:35 2017 +0400

    Add description for nodes section

    Change-Id: I16462dc851c46262bbb43a109cc5bb1380a6ca3e
    Closes-Bug: #1660326