Add supported SSL / TLS protocols check.

This metrics probes the provided hostname for the supported SSL and TLS protocol versions.

Example output:

```bash
$ ./ssl_protocols_check.sh www.google.com 443
metric ssl_2_0 string unknown
metric ssl_3_0 string yes
metric tls_1_0 string yes
metric tls_1_1 string yes
metric tls_1_2 string yes
status Supported protocols: ssl_3_0,tls_1_0,tls_1_1,tls_1_2
```

In ideal world, those metrics would be exposed with `remote.http` or a different remote check.