Dynamic vars with tasks

[hans-d]

Allow vars/envs to be dynamic with output from another task, not just shell commands.

vars:
   BLAH:
      task: :some:other:task
   FOO:
      sh: echo {{.BLAH}} | grep x
   BAR:
      task: :yet:some:other:task
      var:
         TARGET: '{{.FOO}}'

[mgbowman]

Any chance we could triage this issue? I could really use this feature and would like to try and implement it.