registry: remove dead Lock* functions
etcd: add Set.PreviousIndex
role: introduce roles and leases
engine: switch from lock to role lease
registry: remove dead locking code
engine: introduce Purge
Merge pull request #640 from bcwaldon/engine-lease

Switch from engine "lock" to "leased" engine leader role
functional: clean up after jonboulle
Merge pull request #642 from bcwaldon/fix-functional

functional: clean up after jonboulle
unit: move multivalue line check into parse func
unit: add tests for parseMultivalueLine
Merge pull request #643 from bcwaldon/test-unit

Add missing test coverage for unit.parseMultivalueLine
machine/resource: add basic resource reservation information