enhance/multi docker test

[VendettaReborn]

🤔 This is a ...

• New feature
• Bug fix
• Performance optimization
• Enhancement feature
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Workflow
• Other (about what?)

🔗 Related issue link

Previous PR(merged): #324

💡 Background and solution

to test the shadow-tls plugin for shadowsocks .etc, there are two ways:

1. combine shadowsocks&shadow-tls binary file together, build and maintain a new one, so we can use the all-in-one image;
2. run shadowsocks image & shadow-tls image together

the later one causes less trouble in the long term, but we need to support the running of multiple docker images at the same time.

📝 Changelog

dev: support running of multiple docker images in docker test

☑️ Self-Check before Merge

in fact, this enhancement is picked from another branch of supporting shadow-tls protocol, the test of it has been done in my ubuntu laptop.

⚠️ Please check all items below before requesting a reviewing. ⚠️

• Doc is updated/provided or not needed
• Changelog is provided or not needed

[ibigbug]

ty!