Upgrade Shuttl to use SDK v1.2.0.

Changes to a custom HTTPS handler according to 6a90d8cbfa9896ab4e2d90b083d1c52910509943 in splunk/com/splunk/HttpService.java.
Merge pull request #138 from rogerhu/fix_shuttl_splunk_auth

Upgrade Shuttl to use SDK v1.2.0.