Refactor can_i_bump, add tests

Signed-off-by: Kris Kelly <kkelly@pivotallabs.com>
Add pingdom decider to can_i_bump

Signed-off-by: Kris Kelly <kkelly@pivotallabs.com>
Add Pingdom decider to can_i_bump

Signed-off-by: Kris Kelly <kkelly@pivotallabs.com>