Setup HDF5 dataset without having data ahead of time

[ajtritt]

Motivation

Add the ability to create a dataset on disk and get access to the handle to the dataset without having to close and repoen a file.

How to test the behavior?

dataio = H5DataIO(shape=(5,), dtype=int)
foo = Foo('foo1', dataio, "I am foo1", 17, 3.14)
bucket = FooBucket('bucket1', [foo])
foofile = FooFile(buckets=[bucket])

io = HDF5IO(self.path, manager=self.manager, mode='w')
io.write(foofile)

foo.my_data.dataset[:] = [0, 1, 2, 3, 4]
io.close()

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

Merging #747 (a9c6fbf) into dev (ef0a800) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #747      +/-   ##
==========================================
+ Coverage   87.47%   87.57%   +0.09%     
==========================================
  Files          44       44              
  Lines        8790     8834      +44     
  Branches     2023     2033      +10     
==========================================
+ Hits         7689     7736      +47     
+ Misses        786      784       -2     
+ Partials      315      314       -1     

Impacted Files	Coverage Δ
src/hdmf/backends/hdf5/h5_utils.py	86.58% <100.00%> (+0.50%)	⬆️
src/hdmf/backends/hdf5/h5tools.py	82.03% <100.00%> (+0.37%)	⬆️
src/hdmf/build/objectmapper.py	92.72% <100.00%> (+0.36%)	⬆️
src/hdmf/data_utils.py	90.22% <100.00%> (+0.34%)	⬆️
src/hdmf/utils.py	96.53% <100.00%> (ø)

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[oruebel]

Overall this looks good to me.

[rly]

Please fix flake8 changes and add a note to the changelog

[rly]

Thanks. LGTM!