dragonboat: bumped version number to v3.3.5

dragonboat: bumped version to v3.3.4

mod: added github.com/stretchr/testify

mod: bumped pebble version

rsm: not to call ManagedStateMachine.Prepare() when saving dummy snap…

…shots

Fixes lni#162

Merge branch 'master' into release-3.3

dragonboat: bumped version number to v3.2.8

dragonboat: bumped version to v3.2.7

dragonboat: bumped dragonboat version to 3.2.6

dragonboat: bumped dragonboat version to 3.2.5