fix container process addr symbolization

[noneback]

Hey, I found some mistakes when I explored this repo. It cannot locate elfs inside a container when symbolizing a container process. I did this pr to fix it (not quite sure if it works for all scenarios)

how to reproduce

1. start a MySQL docker container process
2. find mysqld process pid ps -ef | grep mysqld, read link /proc/{pid}/root and you will find it links to '/'