Add support for single and double dash prefix flags

[dlamarmorgan]

If storj-up is used to add flags to a service, currently only flags with double dash prefix are supported. The command should be either flexible enough to specify whether to use single dash or double dash, or smart enough to figure it out on it's own.

[ifraixedes]

Why do we want to do that?

Most of the tools that I use have a specified syntax for flags (1 or 2 dashes) and they don't accept to use both syntaxes.

[dlamarmorgan]

Sorry I should have made this ticket more clear.

This ticket is not for storj-up to accept single and double dash prefix as parameters. This ticket is for the storj-up flag command to support adding either single or double dash prefixes to the services it is modifying.