Have main exit with a return code
Have main exit with a return code

This is done in the manner recommended by the API docs for exit().

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

mulkieran/stratisd,stratis-storage/stratisd,trgill/stratisd,trgill/stratisd,mulkieran/stratisd,stratis-storage/stratisd,stratis-storage/stratisd