fix: use go-based powerline-shell

[olevski]

Switch powerline shell to go.

[olevski]

I tested this on the project where previously the terminal prompt was hanging. It does not behave this way with the new powerline shell.

[olevski]

@rokroskar I ran the problematic project again with the go powerline shell (btw the project is from Firat and it is not public). I cannot get the shell to hang at all. Even when I start the session immediately as soon as it is ready, then open one shell run git lfs pull and open other shells while the LFS files are downloaded. Also it seems that as soon as I ran git lfs pull I could also run git status successfully. Or perhaps the new sessions I launched got lucky and avoided whatever problem was causing git status to take forever to run.

As for needing the powerline fonts here is the relevant part from the repo/instructions:
https://github.com/justjanne/powerline-go#installation

Namely it says:

If you want to use the "patched" mode (which is the default, and provides improved UI), you'll need to install a powerline font, either as fallback, or by patching the font you use for your terminal: see powerline-fonts. Alternatively you can use "compatible" or "flat" mode.

Our old config used compatible mode so I used compatible mode here as well.

[rokroskar]

This does not fix #357 - I still get it to hang because the git prompt needs to call git status and git is rebuilding the index for some reason. But we should still switch to the powerline-go implementation, I'm all for that.

[rokroskar]

For me, starting a local session hangs the terminal with this project: https://renkulab.io/projects/rok.roskar/adore

I do renku session start, then first I got a message about "dubious repository ownership" and after fixing that I do docker exec -ti <container-name> bash and the shell hangs. Going into the container with sh I can run top and see

  891 jovyan    20   0  721448  13516   7340 S   5.3   0.1   1:20.70 git-lfs
 1057 jovyan    20   0  721704  13924   7596 S   5.3   0.1   1:10.31 git-lfs
 1134 jovyan    20   0  721448  14928   8440 S   5.0   0.1   1:08.39 git-lfs
  889 jovyan    20   0    7660   4148   3760 S   0.7   0.0   0:10.88 git
 1055 jovyan    20   0    7660   4148   3760 S   0.7   0.0   0:10.11 git

(edit: I tried it with the new image from this PR)

[olevski]

@rokroskar funny enough using this definitely prevents the shell hanging in Firat's project in a session in the web ui. Because I can consistently get the terminal to hang when the old powerline shell is used and it never hangs with the new one.