nuageinit: launch post network script with postnet citype

Sponsored by: OVHCloud

nuageinit: add a post network script

refactor nuageinit to allow a 3rd execution point during boot:
1. nuageinit is invoked before NETWORKING with a minimalistic network setup
for openstrack and

nuageinit: add a post network script

refactor nuageinit to allow a 3rd execution point during boot:
1. nuageinit is invoked before NETWORKING with a minimalistic network setup
for openstrack and potentially other network config setup. it tries
to configure everything which is not requiring any network.
2. nuageinit is invoked again post NETWORKING but pre SERVERS, in the
phase it does all that requires network, like dealing with packages.
Note that creating users have been moved to this phase to allow the
installation of shells like bash or zsh prior the creation of the
users, before that the user creation was failing if a non installed
shell was requested.
3. nuageinit will execute at the rc.local time all the specified scripts
and commands.

MFC After: 1 week

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