generic.test: update invalid_para_mq test

updates:
    1. fix pep8 issue
    2. update step to check both upper and lower border values.
    3. add step to check qemu process coredump.
    4. add step to remove tap device from swith in the end of test if
       netdst is openvswtich.

Signed-off-by: Xu Tian <xutian@redhat.com>
'+' can be removed.