Feature: #686 - Hosts can inherit environment from hostgroup

http://projects.theforeman.org/issues/686

A better explanation:

When you select a group of hosts, there is a button to clear the environment. This leaves all of the hosts with no environment (expected behaviour of course). Nonetheless, we've been lacking of some way to inherit the environment from the hostgroups, which are sort of the 'default' properties for the hosts they own. In fact, if you edit a host and leave the environment empty, it will inherit it from its hostgroup (if any). 

This button provides this inherit behavior from the multiple hosts selection dialog.