Clean up and reorgnize the bpf Test

Code clean up performed on bpf_test.py to make it simplier and
reorgnized the old bpf test to make each test independent from each
other.

Signed-off-by: Chenbo Feng <fengc@google.com>
Bug: 30950746
Test: Test should pass on corresponding kernel
Change-Id: Idb8e77a8822117eabead9fc044f48bbf8f489e8a