ubuntu-restricted-addons is a multiverse package and is not included in
the pool. Therefore, trying to get it installed when offline leads to an
obvious error.
Instead of making the whole Ubuntu installation fail, we now warn and
skip installation of the package when performing an offline install.
In a perfect world, we should not have offered to install the package in
the first place, but in practice, we can run an offline installation as
the result of failed mirror testing (bad network for instance).
Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>
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