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
nexedi/slapos.buildout!26)

See merge request nexedi/slapos.core!376