selftests/tc-testing: update test definitions for local resources

With resources localized on a per test basis, some tests definitions
either contain redundant commands, were wrong or could be simplified.
Update all of them to match the new requirements.

Tested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

selftests/tc-testing: add selftests for pfifo_fast qdisc

Test 900c: Create pfifo_fast with default setting
Test 7470: Dump pfifo_fast stats
Test b974: Replace pfifo_fast with different handle
Test 3240: Delete pfifo_fast with valid handle
Test 4385: Delete pfifo_fast with invalid handle

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>