testcase: support individual build

[mahjonp]

Signed-off-by: mahjonp [email protected]

What problem does this PR solve?

This PR supports the individual builds of test cases.

What is changed and how does it work?

When execute make init c=xxxx to make a new test case, the tipocket scaffold also creates a Dockerfile under that case directory by default which enables each test case to wrap its software dependencies(e.g. sysbench, go-tpc, etc.) on the docker image.

Besides, I decide to open individual builds for newcomer cases since the size of the all-in-one image gets larger and larger when we continually add new cases :(

Check List

Tests

• Unit test
• E2E test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has Go code change
• Has CI related scripts change
• Has Terraform scripts change

Side effects

• Breaking backward compatibility

Related changes

• Need to update the documentation

Does this PR introduce a user-facing change?:

NONE