Increase multiplexer timeout in tests

Some tests (for the Gears module) seem flaky, they fails sometime with
RedisTimeoutException. Try to double the timeout in the connection
multiplexer, from 5 to 10 seconds, hopefully this helps.

Author: Gabriel Erzse

tests/NRedisStack.Tests/RedisFixture.cs

@@ -32,6 +32,8 @@ public RedisFixture()
 
                 ConfigurationOptions clusterConfig = new ConfigurationOptions
                 {
+                    SyncTimeout = 10000,
+                    AsyncTimeout = 10000,
                     EndPoints = endpoints
                 };