add get_root_dir_name to io_utils

[mspector]

In trying to port some closed source code from aida-tools to an open source repo, I discovered this function, with the comment "move to vistautils?"

This PR answers that question with a "yes"

https://github.com/isi-vista/aida-tools/blob/master/aida_tools/utils.py#L75

[codecov]

Codecov Report

Merging #140 into master will increase coverage by 2.38%.
The diff coverage is 7.69%.

@@            Coverage Diff             @@
##           master     #140      +/-   ##
==========================================
+ Coverage   84.20%   86.59%   +2.38%     
==========================================
  Files          25       25              
  Lines        2558     3498     +940     
==========================================
+ Hits         2154     3029     +875     
- Misses        404      469      +65     

Impacted Files	Coverage Δ
vistautils/io_utils.py	88.31% <7.69%> (-3.56%)	⬇️
vistautils/attrutils.py	0.00% <0.00%> (ø)
vistautils/scripts/directory_to_key_value_store.py	97.14% <0.00%> (+0.71%)	⬆️
vistautils/parameters.py	86.38% <0.00%> (+0.89%)	⬆️
vistautils/range.py	94.63% <0.00%> (+1.13%)	⬆️
vistautils/span.py	91.39% <0.00%> (+5.11%)	⬆️
vistautils/key_value.py	92.27% <0.00%> (+9.39%)	⬆️
vistautils/scripts/split_key_value_store.py	86.84% <0.00%> (+22.13%)	⬆️

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[mspector]

No need to review this yet until I resolve code coverage issues