Update Zenmap to consider the -v0 option

[lymanZerga11]

Done with reference to #601. Zenmap does not consider the -v0 option as NmapOptions.py simply uses the arg and renders multiple copies of -v as @dmiller-nmap mentioned.

In this fix, self["-v"] has been assigned the value of -1 for the case of -v0 because,

1. Default value for self["-v"] has been set to 0 (when there is no option "-v" in the command itself).
2. In render() , opt_list does not include "-v" if self["-v"] is 0

[dmiller-nmap]

@lymanZerga11 Thanks for this! I merged it as r36534. Please let me know if you want to be credited under a different name in the CHANGELOG.

[lymanZerga11]

Haha nice! No, this should be fine.