containers: moved some helpers to nixperiments

These helpers are going to be improved independently, so they moved to
a new repository (under the same MIT license).
They are imported from a fixed git commit.
Status Job ID Name Coverage
  Build
failed #1464
build

 
  Test
skipped #1466
allowed to fail
code_quality
skipped #1465
test
 
Name Stage Failure
failed
build Build There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job trace