* Host-generator template is generating a null value like below when host
catalogue is not having any mac value for the interface.
ethernet_mac_address: <no value>
* added another condition to ethernet_mac_address generation logic
so generate only if macAddresses is provided and if it has
value for the respective interface ( oam, pxe ...)
Closes: #404
Change-Id: I2fafe5ceaa4c58855a17929c1c41d60045d1675a