Play Framework

[#1935] Don't create CPU*2 Netty threads for unused ports

This change avoids creating ServerBootstrap objects which are never
bound to a port (for example, not to create the HTTPS server if the
application doesn't configure https.port).  Netty creates
2*(number of processor) "New I/O worker" threads when a
NioServerSocketChannelFactory object is created, so this change
avoids creating lots of threads that the application never uses.