manage kernels in common lib rather than each provider

[osallou]

Currently, we have in each provider, when managing image packages:

    # In squeeze, we need a special kernel flavor for xen
    kernels = {'squeeze': {'amd64': 'linux-image-amd64',
                           'i386':  'linux-image-686', },
               'wheezy':  {'amd64': 'linux-image-amd64',
                           'i386':  'linux-image-686', }, }

For later maintenance, it would be nice to manage this via a kernels.get(xx) or something like that to avoid modifying all providers to add Jessie for example.

globally, Host and Image packages could be put in a common task, called only with a specific list per provider.

[andsens]

Tomasz did something along those lines for some other stuff: 3bc47f6
This could work for kernel images and AKI IDs as well.