crtools: Fix -v option to conform to common sense

The -v option is declared as "optional argument" and thus
only -v=N or -vN are valid. Currently used -v N syntax no
longer works as expected, this will be treated as LOG_ERR
level (single -v) with dangling (unparsed) argument.

Sorry for that :( but it's better to this earlier.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>