restapi: Add CustomProperties member to HostNIC

Added a new Properties member to HostNIC, as well as updated its
mapper (and corresponding test class) to reflect it. Also updated the
Setup Networks entry in rsdl_metadata.yaml to include the new
argument.

Change-Id: Ie1cd53d4e3fd0d2f0d7bec7f1a480679a31c6c8f
Signed-off-by: Lior Vernia <lvernia@redhat.com>