registry: return error from DestroyJob
registry: update job when migrating legacy payload
systemd: log length of unit being written
agent: use correct Job object in LoadJob task

Fix #737
Merge pull request #738 from bcwaldon/737

Carry actual unit file into Agent LoadJob task
etcd: refactor TLS configuration

Separate reading files from creating a TLS config object.
Merge pull request #734 from bcwaldon/migrate-payload-job

registry: update job when migrating legacy payload
Merge pull request #731 from bcwaldon/refactor-etcd-tls

etcd: refactor TLS configuration
registry: remove CheckJobPulse from interface
registry: use available data to determine Job.State

Remove two unnecessary etcd requests by using the data
that is already available on the Job model passed
to determineJobState.
registry: minimize requests to get Job from Registry
bump: github.com/coreos/go-sytemd/*
registry: use unitModel for Unit serialization
job: drop unused method IsOneshot
api: use "schema" as schema name

This makes the schema generator create the schema file
with the correct package name.
engine: remove superfluous state
engine: tweak lease logging
Merge pull request #744 from jonboulle/fix

engine: remove superfluous state
engine: limit reconciliation duration

A reconciliation attempt should stop when the lease is no longer
held by a given agent to prevent conflict with other engines.
engine: make reconcile interval configurable