Add codercom/ubuntu-dev-llvm8 docker base image

[linux-china]

LLVM & Clang are very import for some development, for example WebAssembly, Rust etc. It's a little complicated to install LLVM 8 on Ubuntu for junior. Now we have codercom/ubuntu-dev-gcc8, and could we add codercom/ubuntu-dev-llvm8 on Docker hub. thanks.

I have tried some LLVM images from docker hub, but these images not based from codercom/ubuntu-dev, still some bugs, for example, sudo command not found, /root/.vscode problem, no "user" account by default.

[deansheather]

Created a PR (link above) that contains an llvm-8 image.

[nathanpotter]

The image should be pushed up to docker hub now

[linux-china]

Great. thanks :) https://hub.docker.com/r/codercom/ubuntu-dev-llvm8