add ability to use slashes in branch names

Now branch names like feature/any will work with init-env and meta-update script

Manual executed tests:

• build-multigraf branch feature/swupdate updated
• unit test testrun execuded:

user@ubuntu:~/cust/multigraf/yk/scripts$ python3 lib/repo.py
test_removeprefix (__main__.TestCommonFuncs) ... ok

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Ran 1 test in 0.000s

OK