This reverts commit 4d6a012c.

This PR removes deepcopying of the job attached to the allocation in the
alloc runner. This operation is called very often so removing reflect
from the code path and the potentially large number of mallocs need to
create a job reduced memory and cpu pressure.

Protect against nil job in new allocation

Job revert

Bumping up Vagrantfile's nomad version

Update constraint.html.md

Fix Distinct Constraint header

Refactor Consul Syncer into new ServiceClient

Fixes #2218