Speed up assign_ips and assign_admin_ips methods

assign_ips assign_admin_ips methods are the bottlenecks during deployment,
changes in this methods reduce execution time near 10 times

* added and correct tests
* added ignored_keys param to diff method to ignore some keys during
comparing two dictionaries, this is good when we are not sure or we are
not able to predict values in dictionary
* improved assign_ips and assign_admin_ips methods

Change-Id: I6b60ff722211ddb634c791fbb700a2e46c7143bc
Closes-Bug: #1384623
Blueprint: 100-nodes-support
Merge "Speed up assign_ips and assign_admin_ips methods"