rpc: Pass GPG_TTY and TERM environment variables

rpc: Pass GPG_TTY and TERM environment variables

gpg-agent can be used instead of ssh-agent to authenticate
against an SSH server, but in order to do so the GPG_TTY and
TERM environment variables need to be passed through.

For obvious reasons, we avoid doing that when no_tty=1 is found
in the connection URI.

https://bugs.debian.org/843863
https://gitlab.com/libvirt/libvirt/-/merge_requests/290

Thanks: Guilhem Moulin <guilhem@guilhem.org>
Thanks: Kunwu Chan <chentao@kylinos.cn>
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>