Discovery: don't accept a dynamic update to min_master_nodes which is larger then current master node count

The discovery.zen.minimum_master_nodes setting can be updated dynamically. Settings it to a value higher then the current number of master nodes will cause the current master to step down. This is dangerous because if done by mistake (typo) there is no way to restore the settings (this requires an active master).

Closes #8321
FunctionScore: RandomScoreFunction now accepts long, as well a strings.

closes #8267
closes #8311
Return 0 instead of -1 for unknown/non-exposed ramBytesUsed()

The accountable interface specifies that such values are illegal

Fixes #8239