Credentials lookup fails

[gesellix]

A docker login helps, but we should handle such cases more gracefully:

Caused by: groovy.lang.MissingPropertyException: No such property: auth for class: java.lang.String
        at de.gesellix.docker.client.authentication.FileStore$_getAuthConfigs_closure1.doCall(FileStore.groovy:23)
        at de.gesellix.docker.client.authentication.FileStore.getAuthConfigs(FileStore.groovy:23)
        at de.gesellix.docker.client.authentication.FileStore.getAuthConfig(FileStore.groovy:17)
        at de.gesellix.docker.client.authentication.CredsStore$getAuthConfig.call(Unknown Source)
        at de.gesellix.docker.client.authentication.ManageAuthenticationClient.readAuthConfig(ManageAuthenticationClient.groovy:66)
        at de.gesellix.docker.client.authentication.ManageAuthentication$readAuthConfig$0.callCurrent(Unknown Source)
        at de.gesellix.docker.client.authentication.ManageAuthenticationClient.readDefaultAuthConfig(ManageAuthenticationClient.groovy:49)
        at de.gesellix.docker.client.authentication.ManageAuthentication$readDefaultAuthConfig.call(Unknown Source)
        at de.gesellix.docker.client.DockerClientImpl.readDefaultAuthConfig(DockerClientImpl.groovy:56)
        at de.gesellix.docker.client.authentication.ManageAuthentication$readDefaultAuthConfig.call(Unknown Source)