- XRootD/SSI/Protobuf errors or CTA Exceptions return error code 1
  (something went wrong with communication or in the frontend)

- User errors return error code 2 (user specified an invalid drive,
  vid, etc.)

- If text output, print error message on stderr and exit with code 2

- If --json output, print error message on stderr, print empty JSON
  array [] on stdout, and exit with code 2

Implement cta-admin disksystem add/ls/rm commands.

cta-admin logicallibrary ls
cta-admin mountpolicy ls
cta-admin showqueues
cta-admin storageclass ls

Fixes race condition: for text stream responses, guarantees that
header is printed before the stream data.

Simple repack on CI

Replaced the map of tape files with a list as the assumption that we have one copy per copyNb is no more valid with repack.

Usage: cta-admin --json <command> <subcommand> <options>

For stream commands only (where each line of the result is sent back in
a protocol buffer), return the results in JSON format instead of a
text table.

Adds better cleanup of Requests. The Send() method is synchronous as
before, for Metadata requests. The new SendAsync() method is for Data
and Stream requests, where the Response is returned asynchronously.

The framework now provides a DataFuture object for the asynch case.
After the Request has been sent, call DataFuture::wait() to clean up the
Request object once all data has been received.