Reset of the default automate domains

The rake script was broken looking for 'datastore' directory
Added support for resetting multiple domains if they exist in
the db/fixtures/ae_datastore directory

@mkanoor Looks like you are including MiqAeYamlImportExportMixin at the top of this file to resolve the ```DOMAIN_YAML_FILENAME``` constant.  I think it would be better to remove the include and fully qualify the reference using ```MiqAeDomain::DOMAIN_YAML_FILENAME```.