Changed template file

The role has been requested to support multiple EtherCat master devices (network interfaces). Since this role needs to be backwards compatible with the previous method of only declaring one interface, ethercat_master_device, it would be good to have a couple of eyes on the re-worked role before merging.

In short, the role now forces the variable ethercat_master_device to be in a list-format in a new variable called ethercat_master_device_list. A 3rd VM has been added in molecule.yml with 2 NICs and host_vars are declared to specify each EtherCat master.