BIGTOP-4540. bigtop-select: distro-select "set all" fails with TypeEror: cannot pickle 'dict_keys' object on Python 3

[magnuma3]

Description of PR

Running "distro-select set all " fails on Python 3:

$ sudo ./distro-select set all 3.6.0
Traceback (most recent call last):
  File "/usr/lib/bigtop-select/./distro-select", line 364, in <module>
    createCommandSymlinks(pkgs, options.rpm_mode)
  File "/usr/lib/bigtop-select/./distro-select", line 260, in createCommandSymlinks
    work_packages = copy.copy(packages)
  File "/usr/lib64/python3.9/copy.py", line 92, in copy
    rv = reductor(4)
TypeError: cannot pickle 'dict_keys' object

The "packages" argument is a dict_keys view (from dict.keys()). On Python 2 this was a list, so copy.copy() worked, but on Python 3 dict views are not copyable via copy.copy() and the fallback pickle path fails.

Fix: convert the view to a list, e.g.

work_packages = list(packages)

Environment: Python 3.9 (EL9), Bigtop 3.7.0-SNAPSHOT.

How was this patch tested?

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