Switch to slapos.recipe.build implementation of environment & shared options

'environment-section' option is dropped.
3 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:47:41

passed SlapOS.Eggs.UnitTest-Master.Python3

00:37:55

passed SlapOS.Eggs.UnitTest-Master.Python2

00:56:31