boto_vpc.route_table_present: avoid exception in testing mode
boto_vpc.route_table_present: avoid exception in testing mode

When there is an attempt to create new (non-existent) route table
with boto_vpc.route_table_present and testing mode is turned on,
the "list index out of range" exception is being throw in
_routes_present().

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt