Default Gateway is set in the wrong file in openSUSE

[Zurdo]

openSUSE's network renderer sets the gateway in `/etc/sysconfig/network/ifcfg-eth0` instead of `/etc/sysconfig/network/routes`.

I'm using openSUSE Leap 15.0, OpenStack build downloaded from [here](https://download.opensuse.org/repositories/Cloud:/Images:/Leap_15.0/images/). The included version of cloud-init is 18.4.

Data source is `nocloud`, using the image generated by Proxmox. Attached.

[Zurdo (zurdos)]

Possibly related to:

 - https://bugs.launchpad.net/cloud-init/+bug/1799301 - SUSE sysconfig renderer enablement incomplete (This bugs sees cloud-init believing it should behave the same in RHEL/CentOS as in openSUSE, assuming /etc/sysconfig/network-scripts exists, when it's just /etc/sysconfig/network in SUSE)
 - https://bugs.launchpad.net/cloud-init/+bug/1733226 - cloud-init-local service fails on SUSE distros (Wicked appears to be unique to SUSE, and it apparently expects the default gateway in `routes` instead of `ifcfg-eth0`. This is another easily overlooked difference when compared to RHEL)

SLES remains untested, but given that the "sles.py" distro loads the "opensuse.py" distro, I expect the same behaviour.

[Ryan Harper (raharper)]

Thanks for filing the issue. the sysconfig renderer does need some updates for opensuse specifically around routes files.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3285