2.1 ha upgrade

This PR fixes rolling upgrades of HA from 2.0 to 2.1.
Upgrades are no longer allowed for HA members to prevent independently upgraded stores.
StoreId enriched with two additional fields: ```upgradeTime``` and ```upgradeId```. They are used to discover independently upgraded stores. StoreId is broadcasted with ```MemberIsAvailable``` message and slave checks all known StoreIds before joining the cluster.