add kernel retrieval support
allow options passed to datacenter.list()

only see this to fetch datacenter information from id,
right now
add output helpers for datacenter and kernel
add command 'gandi vm kernels [match]'

--datacenter to filter by datacenter
--flavor to chose kernel flavor
--vm to list available kernels for that vm

add a filter argument for matching, ie. gandi vm kernels 3.2
Add documentation for gandi vm kernels
add kernel param type

the actual disk.list_kernels() requires a datacenter id, and
would induce many calls. We use image.list() : it is very
hackish as it will prevent user from using orphan kernels.

I'm not sure what to do here.
add kernel parameter to disk update
add cmdline parameter to disk update
add documentation to gandi disk update
add metavar for usage information
reorder arguments to avoid compat issues/ugliness
apply review comments (python3, useless uses of..)
Merge branch 'master' into kernels
Merge branch 'master' into kernels
introduce filtered_list, move filtering in the module

command is responsible for the vm fetch (iaas.info) so we
avoid dc dependancy to iaas.

list(options=None) seems pretty std, so introduce filtered_list
for this specific usage. Should take anything with a datacenter_id
as a second optional argument.
Merge pull request #20 from kalou/kernels

New command 'gandi vm kernel' to list available kernels
Update 'gandi disk update' command to allow update of cmdline or kernel