Added --skip_ssl_cert_check option

This will enable qds.py and the qubole sdk to be used against Qubole API servers having self-signed certs. This is useful for internal, test-oriented Qubole deployments that don't need valid CA certs. 

The default value of  "skip_ssl_cert_check" is false, which will always verify the certificate (which is the current behavior). 

Ran some basic tests with the new option enabled/disabled against https/http and against self-signed certs and valid CA certs. All combinations are working.