slurm 20.11: ReqGRES deprecated in favor of ReqTRES

[rkdarst]

• In #7, we got a report that new slurm uses gpu= instead of gpu:. Adjust regex to work with both.
• Also, AllocGRES is deprecated, instead it would be Alloc/ReqTRES.
  • On Slurm >= 20.11, don't request the ReqGRES field and instead use only the ReqTRES field.
  • Also begin requesting ReqTRES even for slurm < 20.11, so that new databases start collecting that data.
• This causes compatibility problems with databases made before this time. So far, we don't promise compatibility, with teh recommend solution being "delete and re-create the database". slurm2sql is not a permenant data store.
• Closes: #7
• Review:
  • check the backwards and forward compatibility assumptions
  • check that it actually works on newer slurm and older slurm

[rkdarst]

No comments, so I will merge and we can fix issues later.