This PR adds an interface for controller API client, it allows us to
implement mock API client for unit testing with ease and we are
able to generate spec file without accessing the real Fission server.
To keep archive creation implementation simple and prevent any
confusion, we decided to remove `--keepurl` flag and embed URL
directly without downloading the file from it . In this way, we can
ensure consistent behavior in either package creation or spec file
creation. Also, it increases the portability of spec file.
Before this PR, CLI functions fatal out when encountering error
instead of returning it. Such behavior makes it hard to reuse
the functions nor writing unit tests. This PR aims to make functions
return errors instead of error out.
In the case of large files, it takes a long time for the user to download
the source from the URL and upload it to StorgeSvc through CLI.
This PR allows a user to use URL as the function source when creating a function
and provides a new flag "--keeparchiveurl" to let the user to decided
whether the CLI should download the file first or store the file URL in the
archive directly. If "--keeparchiveurl" is true, then no checksum will be
generated, it's the user's responsibility to ensure the file won't be changed.
