TESTS: Add a helper binary that can trigger the SIGPIPE to authorizedkeys
Adds a test tool that simulates the behaviour of OpenSSH in the sense
that it starts to read the output from the sss_ssh_authorizedkeys tool,
but then closes the pipe before reading the whole output.
Related:
https://pagure.io/SSSD/sssd/issue/3747
Reviewed-by: Fabiano FidĂȘncio <fidencio@redhat.com>