Re-schedure test case sequence in network basic test suite.

[Botao]

For network basic test suite, a re-schedule of test case sequence is now required to avoid expected failure, such as ping test after network interface turned down.

Sometimes the "ifconfig eth0 down" doesn't work on some boards, which results followed test case passed. However, this should not be considered as a common practice.

The latest example on ARM Versatile Express Linux Linaro ubuntu daily test shows that after ifconfig down test performed, both ping test and curl test for video sample file downloading failed.

https://validation.linaro.org/dashboard/streams/private/team/linaro/pre-built-vexpress/bundles/d2875e00e102d24a302dcd4e80d4320a8bece145/362629e5-2b39-4b9e-ae6e-3bc6dda3c4a0/

[Chase Qi (chase-qi)]

Migrated to bugzilla: https://bugs.linaro.org/show_bug.cgi?id=591