slapos cli: add slapos cachelookup commands

This commit remove the following 2 commands:

• slapos cache lookup
• slapos cache source

And introduces the following 3 commands:

• slapos cachelookup binary-sr
• slapos cachelookup url
• slapos cachelookup pypi

This is useful to check if some objects are in shacache for buildout. Please note that the commands are using the latest keys (introduced in https://lab.nexedi.com/nexedi/slapos.buildout/merge_requests/26)