version: bump to v0.7.1+git
functional: simplify nspawn machine creation

Generating all SSH host keys every time we spin up a machine is
slow and unnecessary. We could consider moving to fixtures, but for now
it's easier to simply generate a single key.

systemd also introduced a hardware database service that was taking a
relatively considerable amount of time, and should be unecessary in a
systemd-nspawn container.

This brings the average machine bring-up to ~1s
doc: fix broken link

Fix #795
test: drop schema from testables
Merge pull request #792 from jonboulle/testz

functional: simplify nspawn machine creation
engine/agent: change reconciler ticker behaviours

The engine/agent currently reconcile every $reconcileInterval,
irrespective of whether any reconcilations occurred for other reasons
(i.e. were triggered) within that period.

A better semantic is for the tick to occur every $reconcileInterval
_after the previous reconciliation was triggered_. To accomplish this,
reset the ticker every time a reconciliation is about to commence.
Merge pull request #798 from jonboulle/reconcilers

engine/agent: change reconciler ticker behaviours
Merge pull request #797 from bcwaldon/test-schema

test: drop schema from testables
agent: add global unit support to reconciler
agent: remove unnecessary TargetMachineID
engine: do not consider global units for scheduling
fleetctl: update to deal with global units

All fleetctl operations on global units are non-blocking. Updated
command descriptions to reflect this.

suToGlobal is shared across commands and so now moved to fleetctl.go

setTargetStateOfUnits should only care about DesiredState, not
CurrentState, of units it is attempting to modify.

Also standardises behaviour and error message reporting across commands
functional: various updates

Update to accommodate multiple UnitStates
Add a simple functional test for global units