This commit is another isolation refactor, this time for repo fork.
However, I got fed up with the --remote="true|false|prompt" style of
flags and took this opportunity to switch to a set of bool flags:
--remote and --clone
--no-remote and --no-clone
the string args were really non standard and confusing; with only two
bools it was impossible to tell when to prompt.
This commit hacks the existing repo clone tests into something usable by
the new isolated command. It went ok and was less effort than trying to
introduce the same kind of test format as repo view and gist create.
When `{owner}` and `{repo}` strings are found in request path (for REST
requests) or `query` (for GraphQL), they are replaced with values from
the repository of the current working directory.
