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
slapos.buildout!26)

See merge request !376