slapproxy: Add minimal hateoas support for cli
Add the minimum hateoas support required to let slapproxy answer the cli commands:
slapos service listslapos service info <reference>slapos computer listslapos computer info <reference>
To enable hateoas, complete the slapos.cfg configuration with:
[slapos]
master_rest_url = <proxyaddr>/hateoas
Also: fix a few small bugs and python3 incompatibilities in slap/hateoas.