py2/py3/deb packages names are case insensitive, and the versions map
key should be the same for packages whose name can have different cases.
For example, in files/build/versions/default/versions-py3, package
"click==7.1.2" is pinned; and in
files/build/versions/dockers/docker-sonic-vs/versions-py3, package
"Click==7.0" is pinned.
Without this fix, the aggregated versions-py3 file used for building
docker-sonic-vs looks like below:
...
click==7.1.2
Click==7.0
...
However, we actually want "click==7.0" to overwrite "click==7.1.2" for
docker-sonic-vs build.
