Dataset problem: CIESM pr

[lee1043]

CMIP6 CIESM precipitation data need to be multiplied by 1000

https://errata.ipsl.fr/static/view.html?uid=d4a11704-808a-5869-b94d-234170eb70ea

ESMValGroup/ESMValCore#471

[lee1043]

While this has been a long standing issue (incorrect units for pr of CMIP6 CIESM model), should PMP correct the data on the fly for the metrics calculation, or leave it as is because it's an upstream issue.

@gleckler1 @kristinchang3 any thoughts?