test/suites/tls_restrictions: don't check for broken pipe error

[simondeziel]

Making a TLS 1.2 connection with an unsupported cipher does not reliably produces a broken pipe error:

for _ in $(seq 100); do
    for cipher in ECDHE-ECDSA-AES128-SHA ECDHE-ECDSA-AES256-SHA; do
        my_curl --tls-max 1.2 --ciphers "${cipher}" -X GET "https://${LXD_ADDR}" -w "%{errormsg}\n"
    done
done 2>&1 | sort | uniq -c
      1 Empty reply from server
    196 OpenSSL SSL_write: Broken pipe, errno 32
      3 OpenSSL SSL_write: Connection reset by peer, errno 104

but it always fail so let not look for a specific error, just make sure the connection fails.