Automatically create needed attributes and attribute namespaces

[0xbase12]

ServiceOffersCommand.py base command should create default attribute namespaces automatically if not found:

• price
• schema-org
• resource

It should also call a specific function defined in each connector to create all needed attribute namespaces and attributes: Example: Exoscale connector should create:

• Namespace exoscale
• Attribute exoscale:instanceType
• Attribute exoscale:XYZ

Remove creation of schema-org from deploy_prs_service function in https://github.com/slipstream/SlipStream/blob/master/install/slipstream.sh#L892