Restart individual nodes in the pipeline

[PetarKirov]

#36 works great for what it's intended to do, but I think over 90% of the spurious failures are due to only dub or vibe.d, so an option restart a leaf node (basically a third-party project a.t.m.) would be very handy.

For example, I had to restart Jenkins because of dub here:
https://ci.dlang.io/blue/organizations/jenkins/dlang-org%2Fphobos/detail/PR-5648/3/pipeline/173
The whole run lasted 09:15 min, while the dub node took about 1:30 mins, meaning this option could save around 7-8 mins.

[wilzbach]

I guess that's going to problematic because the compiler gets built in the first stages which is used for the further stages and I guess these binaries aren't saved. I don't know much about Jenkins though.

[MartinNowak]

Not possible and hardly ever will be supported, pipelines are just too configurable.
Don't be worried to just restart the whole pipeline, resource usage is fairly small atm.