network: Drop UUID handling for default network

network: Drop UUID handling for default network

We are generating a fresh UUID and storing it in the XML for the
default network, but this is unnecessary because the network
driver will automatically generate one if it's missing from the
XML; the fact that we only do this if the uuidgen command happens
to be available on the build machine is further proof that we can
safely skip this step.

This patch is best viewed with 'git show -w'.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>