objectquery: factor out sysimage prep

This moves system image preparation out of the `ObjectQueryMiddleware`
and into a util function in called `get_zerovm_sysimage_devices`.
Merge pull request #128 from larsbutler/code-cleanup

Code cleanup
fix leaking of unneeded headers to applications

`X-Storage-Token` and `Cookie` headers were leaked into CGI environment
There is no need for an application to know that information
Merge pull request #131 from pkit/bug_fix

fix leaking of unneeded headers to applications