add dockerized tube for better pwning

When pwning(especially heap challenges), I sometimes want to make docker environment, put all challenge files, execute and debug with pwntools enabled.

Maybe this process can be automated by adding process-like tube (I called it `dockerized`)

```python
from pwn import *

context.log_level = 'debug'

if __name__ == "__main__":
p = dockerized('./realloc', baseimage='ubuntu:18.04', prefer_dockerfile=False)
gdb.attach(p)
p.interactive()
```

I made similar feature in https://github.com/ohk990102/pwntools-addon-dockerized, and hope this can be added in pwntools too.