Reroute Allocate to force primary allocation when enabled
Typically, the main reason a reroute allocation command with allow_primary is enabled, is to force create an empty new shard because a shard (and its replicas) were lost. This can't be done today because the shard expects to have a valid index where its allocated, we need to clear its post allocation flag to make sure it is allowed to create a fresh index.
Make GetField behavior more consitent for multivalued fields.

Before this change, the GetField#getValue() method was returning a list of values of a multivalued fields if the field values were obtained from source or if the field was stored and real-time get was used. If the field was stored but non-realtime get was used, GetField#getValue() was returning only the first element and the GetField#getValues() was returning a list of elements. This change makes behavior consistent. GetField#getValue() now always returns only the first value of the field and GetField#getValues() returns the entire list.