Mark host frames as not needing to be writeable

[jakirkham]

Partially addresses issue ( dask/distributed#3994 )

Leverages a feature in Dask to bypass copying of frames on host. ( dask/distributed#4004 ) This can offer a notable speed up when working with "dask" serialization.

cc @quasiben

[codecov]

Codecov Report

Merging #5824 into branch-0.15 will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           branch-0.15    #5824      +/-   ##
===============================================
+ Coverage        84.06%   84.38%   +0.32%     
===============================================
  Files               80       80              
  Lines            13066    13387     +321     
===============================================
+ Hits             10984    11297     +313     
- Misses            2082     2090       +8     

Impacted Files	Coverage Δ
python/cudf/cudf/core/abc.py	91.48% <100.00%> (+3.39%)	⬆️
python/cudf/cudf/io/feather.py	100.00% <0.00%> (ø)
python/cudf/cudf/comm/serialize.py	0.00% <0.00%> (ø)
python/custreamz/custreamz/_version.py	0.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/_version.py	0.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_orc.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_json.py	100.00% <0.00%> (ø)
...ython/dask_cudf/dask_cudf/io/tests/test_parquet.py	100.00% <0.00%> (ø)
python/cudf/cudf/utils/applyutils.py	98.75% <0.00%> (+0.02%)	⬆️
python/cudf/cudf/core/join/join.py	92.41% <0.00%> (+0.03%)	⬆️
... and 30 more

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[jakirkham]

PR ( dask/distributed#4004 ) is now in. This should be good to go 😄