adds configurable timeout to endpoint

[MishaConway]

[lucasklaassen]

@MishaConway did you happen to run into an error like this:

SocketError: getaddrinfo: Try again                                                                                                     
  /app/vendor/bundle/ruby/2.6.0/gems/dalli-elasticache-0.2.0/lib/dalli/elasticache/auto_discovery/endpoint.rb:64:in `initialize'        
  /app/vendor/bundle/ruby/2.6.0/gems/dalli-elasticache-0.2.0/lib/dalli/elasticache/auto_discovery/endpoint.rb:64:in `new'               
  /app/vendor/bundle/ruby/2.6.0/gems/dalli-elasticache-0.2.0/lib/dalli/elasticache/auto_discovery/endpoint.rb:64:in `remote_command'    
  /app/vendor/bundle/ruby/2.6.0/gems/dalli-elasticache-0.2.0/lib/dalli/elasticache/auto_discovery/endpoint.rb:47:in `get_stats_from_remo