(maint) Sign certificates used in testing

On versions of OpenSSL around version 0.9.8y, it was possible to decode certificates
that had not been signed. However OpenSSL 1.0.1i cannot decode unsigned
certificates. Given the following PEM encoded cert:

    -----BEGIN CERTIFICATE-----
    MIGqMIGgoAMCAQICAQAwAgYAMAAwHhcNMTQxMDAxMTgzNTQ5WhcNMTQxMDAxMTkz
    NTQ5WjASMRAwDgYDVQQDDAd0ZXN0aW5nMFwwDQYJKoZIhvcNAQEBBQADSwAwSAJB
    ALiOQvoQaSIRDogCJwLKmM11vObOnBm93AdGkezbpdHI/TFebvvZYT2J6ukPmyVD
    bGa0ZEpg5gc2yJ+sgJTwbSsCAwEAATACBgADAQA=
    -----END CERTIFICATE-----

When printed to text this results in the following:

    Certificate:
        Data:
            Version: 3 (0x2)
            Serial Number: 0 (0x0)
        Signature Algorithm: NULL
            Issuer:
            Validity
                Not Before: Oct  1 18:35:49 2014 GMT
                Not After : Oct  1 19:35:49 2014 GMT
            Subject: CN=testing
            Subject Public Key Info:
                Public Key Algorithm: rsaEncryption
                    Public-Key: (512 bit)
                    Modulus:
                        00:b8:8e:42:fa:10:69:22:11:0e:88:02:27:02:ca:
                        98:cd:75:bc:e6:ce:9c:19:bd:dc:07:46:91:ec:db:
                        a5:d1:c8:fd:31:5e:6e:fb:d9:61:3d:89:ea:e9:0f:
                        9b:25:43:6c:66:b4:64:4a:60:e6:07:36:c8:9f:ac:
                        80:94:f0:6d:2b
                    Exponent: 65537 (0x10001)
        Signature Algorithm: NULL

OpenSSL 1.0.1i can convert the certificate to PEM and DER, but it cannot
decode it. Decoding the PEM encoded text directly as a cert results in
the following error:

    OpenSSL::X509::Certificate.new(minimal_certificate.to_pem)
    OpenSSL::X509::CertificateError: nested asn1 error

Decoding the DER encoded cert as raw ASN1 results in the following:

    OpenSSL::ASN1.decode(minimal_certificate.to_der)
    OpenSSL::ASN1::ASN1Error: invalid object encoding

So OpenSSL is convinced that we have a mangled certificate.

The solution to this to self-sign the certificate, so that the
certificate can be properly encoded and decoded.