Using Cate monitor with deferred processing

[JanisGailis]

Expected behavior

Any operation that has the potential of running for some time should accept a monitor to give feedback about progress and provide the ability to cancel it.

Actual behavior

When using xarray ufuncs and arithmetic capabilities, the actual processing is deferred until data is actually accessed - plotted, printed, explicitly accessed through .values. Currently there is no way how to inject Cate monitor into xarray/dask land to perform monitoring, or cancel the task.

Specifications

Cate 0.9.0.dev3

[JanisGailis]

We probably have to leverage this in some way:
http://dask.pydata.org/en/latest/diagnostics.html