fix: python prevent infinite loop

[zvigrinberg]

Description

For python pip requirements.txt stack analysis:
In case there is a Cyclic reference in python pip dependency tree , then without detecting it and "cut" the cycle, resolving the dependency tree will never end and the API will enter into infinite loop.
So in every case there is a cycle in the dependency tree, detect it, and cut it.

Example

for example, consider sphinx and sphinxcontrib-applehelp, each one is a dependency of the other , as can seen from the following pip show command of both of packages:

Fix: https://issues.redhat.com/browse/TC-671

Checklist

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Additional information

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