Allow specifying a host on which to listen even with SSL
Grab the IP address from the HOST environment variable and use it to bind the SSL server.
Default to 0.0.0.0
IPv6 compliant.
The two chained stat() promises may not have finished by the time
`enableSSL` is evaluated in case of a slow file system (e.g. on a
Raspberry Pi where the only block device is an SD card).