[finishes #51421573] reorg of system_micro tasks, explicitly call rake tasks, and remove obsolete stemcell promotion
[finishes #51421573] reorg of system_micro tasks, explicitly call rake tasks, and remove obsolete stemcell promotion

Signed-off-by: Sean Sweda <27f6c7115828598484b147fe20383cd4698e1a0e@pivotallabs.com>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh