Change default behaviour of the snetd

[raamb]

1. May be it makes sense to rename serve to start command as it should be more obvious.
2. I think it is not required to keep serve (or start) as default behavior, I think now it is time when we can replace all usages by explicit snetd-linux-amd64 start especially if it is confusing.

Originally posted by @vsbogd in https://github.com/singnet/snet-daemon/pull/143

[anandrgitnirman]

so the conclusion here is to replace serve by start ? and ensure you pass the param start to start the Daemon ?

[ferrouswheel]

I would recommend staying with serve unless we are splitting snetd into a control application and a separate daemon.

When a utility uses start I expect it to start a daemon and return to the command line. And I think of it being a startup script that controls a daemon in the background. e.g. init scripts or systemd

serve is not a new command, jekyll uses it to run a server, as do other tools.