Change logic of get networks in attach_to_networks
Change logic of get networks in attach_to_networks

In attach_to_networks method replace get_networks method to
   get_network and loop. This behavior save order of nets
   which setted via system environment.

Change-Id: I2186acbae44aa64dab311bd1224e1c7540547a63
Closes-bug: #1456288
Closes-bug: #1444058
Closes-bug: #1454786

stackforge/fuel-devops,stackforge/fuel-devops