feat(storage): API support for storage settings

[joseivanlopez]

A JSON schema for the storage config is defined by #1455. This PR adds support to the D-Bus API to allow setting a JSON config following that new JSON schema:

org.opensuse.Agama.Storage1
  #SetConfig s
  #GetConfig s

#SetConfig

For now, the #SetConfig D-Bus method admits 3 different JSON formats for the given JSON config:

• Guided config

{ "storage": { "guided": ... } }

• New storage config

{ "storage": { ... } }

• Legacy AutoYaST config

{ "legacyAutoyastStorage": [ ... ] }

The plan is to make #SetConfig and #GetConfig only to work with a storage config or a legacy AutoYaST config. The guided config is still accepted by #SetConfig because the new storage config does not offer all the options offered by guided config yet.

In the future, the guided config will be neither accepted nor reported by #SetConfig and #GetConfig respectively. Nevertheless, a D-Bus method accepting the guided config will still be offered as a simplification of the storage settings to make easier to work with the use cases supported by the web UI.

#GetConfig

Currently, #GetConfig reports different config formats depending on how the proposal was calculated:

• For the initial proposal: reports the guided config.
• If #SetConfig was called with guided config: reports guided config (extended with mandatory volumes, etc).
• If #SetConfig was called with storage config: reports exactly the given storage config.
• If #SetConfig was called with legacy AutoYaST config: reports exactly the given legacy AutoYaST config.
• If Storage1.Proposal#Calculate was called: reports the guided config (extended with mandatory volumes, etc).

In the future, #GetConfig will only report either the storage config or the legacy AutoYaST config.

[coveralls]

coverage: 71.68% (+8.3%) from 63.343%
when pulling 3e1c2ee on joseivanlopez:api-storage-settings
into 10093da on openSUSE:master.

[ancorgs]

Re-approved after changelog fix.