update das-selected-lumis script to match the new das server format

[smuzaffar]

Looks like DAS server now returns
"data": [{"lumi":{"number":[]}}]
instead of
"data": [{"lumi":[{"number":[]}]}]
adopt the das-selected-lumis.py script to handle both cases

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for master.

It involves the following packages:

Configuration/PyReleaseValidation

@kkousour, @kpedro88, @fabozzi, @cmsbuild, @GurpreetSinghChahal, @davidlange6 can you please review it and eventually sign? Thanks.
@makortel, @felicepantaleo, @ebrondol, @ghellwig, @Martin-Grunewald this is something you requested to watch as well.
@davidlange6 you are the release manager for this.

cms-bot commands are listed here

[davidlange6]

merge

[cmsbuild]

backport failed
Reason:

Error: Failed to cherry-pick commits. Please backport this PR yourself.

mark the corrected paths with 'git add <paths>' or 'git rm <paths>'
and commit the result with: 

        git commit -c 7c829c3281b9024fd106fb61520faf2b3055744c