Bugfix for 'reset-roles' argument handling

Vagrant now includes the subcommand itself in @argv, so the @argv.empty? check
in the reset-roles command is never true. Checking that the length is greater
than 1 would match the old behavior exactly but at the cost of
backward-incompatibility.

Change-Id: I2780abb611fc5a07b65a61150674e23648e3e9b7
Merge "Bugfix for 'reset-roles' argument handling"