add command line option for version

[piccione99]

Currently if you run xmidt-agent --help, you get below:

mpicci200@RESML-1722218 xmidt-agent % ./xmidt-agent --help
Usage: xmidt-agent [flags]

The cpe agent for Xmidt service.

Version:  undefined
Date:     undefined
Commit:   undefined
Built By: undefined

Not sure if these values are just not hooked up or you need a release version. Eithe way, --version is pretty standard and should probably be an option