Add subjectAltName support

[diafygi]

This script should be able to find and validate multiple subject alternative names in one csr.

user@hostname:~$ export SAN="subjectAltName=DNS:example.com,DNS:www.example.com"
user@hostname:~$ openssl req \
>     -new \
>     -key domain.key \
>     -sha256 \
>     -subj "/" \
>     -reqexts SAN -config <(cat /etc/ssl/openssl.cnf <(printf "[SAN]\n$SAN")) \
> | openssl req -text -noout
Certificate Request:
    Data:
        Version: 0 (0x0)
        Subject: 
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:a8:05:50:86:49:98:c8:05:01:e9:50:18:7f:2f:
                    b4:89:09:29:d1:c1:58:d8:14:bb:58:1d:25:50:11:
                    bb:43:d8:28:03:a5:de:59:49:bb:d2:f7:d3:79:5c:
                    c6:99:2c:98:ff:99:23:8c:df:96:7c:ea:4b:62:2a:
                    a4:c2:84:f5:5d:62:7f:7d:c4:7c:e2:c3:db:e6:58:
                    03:c2:26:9d:02:da:bb:84:d9:11:82:fe:38:12:9b:
                    c7:b6:ff:b2:40:30:38:b1:44:d8:47:1d:43:4a:29:
                    58:6b:49:ec:33:d7:dc:a7:1b:90:05:3a:f5:e6:16:
                    98:08:5d:2d:7e:b4:ea:a2:a4:b1:84:89:f7:f1:c4:
                    67:a6:a1:06:70:dd:4e:6b:0c:f8:b5:9b:bc:3f:06:
                    ee:90:d6:86:29:52:d3:af:f6:d4:2f:c6:cf:4b:5a:
                    b8:cd:01:74:6d:5c:25:a8:02:1c:7c:e8:66:3d:46:
                    07:b1:9d:ef:cc:eb:90:b6:bf:7b:33:e0:5f:b2:9b:
                    e8:b4:12:67:2f:8d:0d:9b:54:9d:95:6e:09:83:cb:
                    f3:5b:1f:31:8e:3b:ca:4e:08:e0:40:c0:60:40:72:
                    dd:0d:3e:99:ec:7c:ac:c4:3c:ba:85:9d:d9:d9:6b:
                    02:2e:bf:a8:a3:02:1d:eb:c8:58:e3:04:b3:a5:f1:
                    67:37
                Exponent: 65537 (0x10001)
        Attributes:
        Requested Extensions:
            X509v3 Subject Alternative Name: 
                DNS:example.com, DNS:www.example.com
    Signature Algorithm: sha256WithRSAEncryption
         99:a5:f0:c3:6d:5c:fc:90:5a:de:3e:3e:15:f1:5c:90:18:48:
         04:26:bb:3e:3a:13:7b:14:93:fe:ff:d4:87:ee:06:8b:f3:82:
         83:54:d8:99:82:48:e3:27:d5:5e:d7:88:2d:c0:70:b6:34:93:
         57:16:c5:7a:8a:3d:38:43:b2:06:21:ee:82:e2:6b:6a:5a:22:
         e0:68:a0:ed:88:d1:a6:42:b7:d4:a0:f6:5d:18:7f:41:f1:3e:
         cf:5c:f8:36:8c:8f:53:db:eb:e6:ac:f9:0d:cd:11:f0:80:84:
         7d:68:14:a9:58:21:40:fb:3e:9c:c8:1d:b0:89:14:f2:a0:55:
         2a:ab:3a:0e:be:12:6b:23:d4:35:84:0c:40:13:c9:bd:cf:5d:
         bf:04:e1:20:01:99:28:fc:58:bf:08:64:ee:8d:b4:35:fc:e9:
         00:70:64:c8:5c:98:0b:6a:56:0e:44:9a:4a:2e:9f:0e:87:1a:
         43:06:0c:40:79:b2:92:34:85:72:d4:db:6b:2a:77:7c:40:02:
         9e:b0:88:2c:41:fc:0e:ed:1d:75:d7:de:4f:09:3c:84:82:ea:
         fe:24:69:5d:af:a4:a9:0f:c8:8f:56:69:13:fa:e4:94:3c:64:
         82:4f:60:e2:46:85:b3:80:a6:74:de:38:e5:75:ba:22:fc:2c:
         a6:9f:af:1b