xci: Networking fixes to introduce role and interface var

xci: Networking fixes to introduce role and interface var

Network configuration task and accompanied handler put into a role
and handler is converted to task.

Distro specific var, interface, is introduced to ensure we do not
hardcode the interface which might not be available.

Update the templates accordingly.

Change-Id: I667620fe22c93a9b20a1d8c1b7b0051d7647b591
Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>