The following patch adds the options "--external" & "--internal"
and the suboptions to "external": "--default" & "--no-default",
to "osc network set" CLI to provide the user an option to set
a network as an external network or remove the setting.
Change-Id: I3a7f2cb249bc8101cbb01322d7732e913237d6cd
Partial-Bug: #1545537