Make ovn-central network interface configurable

Make ovn-central network interface configurable

installer.sh script is configuring ovn-central address <ip>:<port>
to environment variable.
Ip address is detected from the ovn-central host through ansible
by grepping ifconfig output, but in this step detected network
interface is hard-coded in the code to be "eth1".

This commit makes network interface configurable in aio/vagrant
deployment.

Issue-ID: MULTICLOUD-621

Change-Id: Icbe22ffdcb45c5f16067ea609eec76fb70c0ea78
Signed-off-by: Samuli Silvius <s.silvius@partner.samsung.com>