refactor(fleet/VerifyJob): abstract it as a function

Make it much clear.
fix(fleet/VerifyJob): check job from EventJobUpdated

When agent gets updated job from etcd, it should check its
signature still.
fix(agent): submit bids for jobs that agent can verify
Merge pull request #196 from unihorn/25

fix(fleet/VerifyJob): check job from EventJobUpdated