Fail fast when importing distributed.comm.ucx (#3228)
Fail fast when importing distributed.comm.ucx (#3228)

Fixes https://github.com/dask/dask/issues/5572

If we don't have UCX installed then we shouldn't try anything further.
In this commit we move the `import ucp` line to the top of the file.
dask/distributed,dask/distributed,dask/distributed,blaze/distributed,blaze/distributed,dask/distributed