Share event-loop-group between client connections

... if the client is free-standing (not invoked from
an existing eventloop), use a shared group.

Author: helje5

Sources/Redis/RedisClientOptions.swift

@@ -14,6 +14,9 @@
 
 import NIO
 
+fileprivate let onDemandSharedEventLoopGroup =
+                  MultiThreadedEventLoopGroup(numThreads: 1)
+
 /// Configuration options for the socket connects
 open class ConnectOptions : CustomStringConvertible {
 
@@ -28,7 +31,7 @@ open class ConnectOptions : CustomStringConvertible {
     self.port     = port
     self.eventLoopGroup = eventLoopGroup
                        ?? MultiThreadedEventLoopGroup.currentEventLoop
-                       ?? MultiThreadedEventLoopGroup(numThreads: 1)
+                       ?? onDemandSharedEventLoopGroup
   }
 
   public var description: String {