etcd: enable SSL Certificate authentication

Provide TLS configuration when SSL certificate authentication is enabled in etcd endpoints.
Add configuration option for keyfile, certfile and cafile on both fleet and fleetctl.
Merge pull request #677 from Deliverous/master

Enable SSL Certificate authentication for etcd endpoint
config: fix typo in sample config
engine: mv dumb-reconciler.go -> dumb_reconciler.go
registry: give Bids a string
offer: ignore partitioned offers
engine: drop unused partitioning code
engine: drop wipReconciler
engine: add clusterState object
engine: use clusterState object
engine: move commands from reconciler to Engine
engine: use task mechanism in reconciliation
agent: update reconcilier logging