json-edit: Support editing arrays

When an element of the path is an integer and the parent attribute is an
array, then we just continue as expected, instead of changing the parent
attribute to a hash and overwriting things.
json-edit: Improve error reporting

We can provide the path to current attribute causing an error.
json-edit: Respect --no-clobber for parent attributes too

If a parent attribute exist, but the full path doesn't exist because the
parent attribute is not a hash or array, respect --no-clobber.
Merge pull request #2070 from dirkmueller/master

Make SLE12 media optional
Merge pull request #2060 from vuntz/json-edit-array

Make json-edit able to edit attributes that are arrays
Update to latest provisioner.json format (bnc#895086)
Merge pull request #2072 from jsuchome/provisioner_repos

Update to latest provisioner.json format (bnc#895086)
Fix Cloud 5 compute channel naming