Merge pull request #22 from humanux/ping

generic.test.ping: make ping test support ipv6
tests.vlan: some issues fix

This patch fix some issues of this script:
1. kill netcat server if any exceptions happens
2. split this test to two
3. make this script follow pep8 rules

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>