Sign RPM with rpmsign.

def AddSignatureToRPMs(self, rpm_filenames):
    """Sign RPM with rpmsign."""
    # The horrible second argument here is necessary to get a V3 signature to
    # support CentOS 5 systems. See:
    # http://ilostmynotes.blogspot.com/2016/03/the-horror-of-signing-rpms-that-support.html
    args = [
        "--define=%%_gpg_name %s" % self.gpg_name,
        ("--define=__gpg_sign_cmd %%{__gpg} gpg --force-v3-sigs --yes "
         "--digest-algo=sha1 --no-verbose --no-armor --pinentry-mode loopback "
         "--no-secmem-warning -u '%s' -sbo %%{__signature_filename} "
         "%%{__plaintext_filename}" % self.gpg_name), "--addsign"
    ] + rpm_filenames

    try:
      output_log = io.StringIO()
      rpmsign = pexpect.spawn("rpmsign", args, timeout=1000)
      # Use logfile_read so we don't get the password we're injecting.
      rpmsign.logfile_read = output_log
      rpmsign.expect("phrase:")
      rpmsign.sendline(self.password)
      rpmsign.wait()
    except pexpect.exceptions.EOF:
      # This could have worked using a cached passphrase, we check for the
      # actual signature below and raise if the package wasn't signed after all.
      pass
    except pexpect.ExceptionPexpect:
      logging.error(output_log.getvalue())
      raise

    for rpm_filename in rpm_filenames:
      try:
        # Expected output is: filename.rpm: rsa sha1 (md5) pgp md5 OK
        output = subprocess.check_output(["rpm", "--checksig", rpm_filename])
        if "pgp" not in output:
          raise SigningError("PGP missing checksig %s" % rpm_filename)
      except subprocess.CalledProcessError:
        logging.exception("Bad signature verification on %s", rpm_filename)
        raise SigningError("Bad signature verification on %s" % rpm_filename)