Remove dependancy on OSG CA certs from Jobsub client
Now that all Jobsub servers have CA certs that have a chain of trust down to a CA included the standard OS and browser bundles, I propose changing the client to use the OS default CA bundle by default. This is one less dependency for users to have to install to use the client, and one less thing to go wrong.
Note that the only thing that seems to be keeping this from working right now when setting
X509_CERT_DIR=/etc/pki/tls/certs (on an SL6 system) is cigetcert, since the jobsub servers on :443 don't present the CA chain, while they do on :8443.