fix(raft_server_stats): set startTime when init

This helps one-node cluster get rid of bogus startTime.
tests(snapshot): expand reasonable range for index

snapshot file was createed with name '0_503.ss' and '0_1010.ss' when testing.
Merge pull request #773 from unihorn/82

tests(snapshot): expand reasonable range for index
chore(config): move Sanitize and Force check to boot process

Make Load function just load parameters. So etcd instance could
use Config struct to start service.
refactor(tests/server_utils): use etcd instance

Remove duplicated etcd start code.
fix(registry): fetch peers from store instead of cache

The current cache implmentation may contain removed machines, so we
fetch peers from store for correctness.
Merge pull request #777 from unihorn/86

fix(registry): fetch peers from store instead of cache
feat(peer_server): add State field to machineMessage

State field indicates the state of each machine.
For now, its value could be follower or leader.
chore(cors): more explanation for flush in ServeHTTP
Merge pull request #776 from unihorn/85

feat(peer_server): add State field to machineMessage
Merge pull request #775 from unihorn/84

refactor(tests/server_utils): use etcd instance
fix(TestV2Watch): ensure server has started
Merge pull request #778 from unihorn/88

fix(TestV2Watch): ensure server has started
Merge pull request #763 from unihorn/77

fix(raft_server_stats): set startTime when init
chore(client): minor changes based on comments

The changes are made on error handling, comments and constant.
Merge branch 'master' of github.com:coreos/etcd

Conflicts:
	server/peer_server_handlers.go