[ci] Jenkins queueing takes forever

[driazati]

e.g. in the job https://ci.tlcpack.ai/job/tvm/job/PR-13256/9/, the actual build took 2.5 hours but the total job run time was over 12 hours.

cc @Mousius @areusch @gigiblender

[driazati]

The autoscaler plugin on Jenkins was getting stuck often, refreshing to a clean state seems to have fixed it