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.

Better to have all formatting on the client side, so we format the
header and the reponse values in the same place. (Also no need to
send this data over the wire as it's always the same).

PB now accommodates "lpa" and "lpr" responses as well as "af ls"

OptionStrList takes a filename as its value. It reads the file into a
list of strings in the protobuf. On the server side, the values are
unpacked and made available as std::vector<std::string>.

For example implementation, see "cta-admin repack add"

Integrates XRootD logging

Default now set to 10s. Note that XRD_TIMEOUTRESOLUTION must be set
<= 10s, otherwise timeout defaults to 15s.