Comment 6 for bug 1773084

Thank you for providing the requested information. Unfortunately the process holding the DPKG lock is already gone in the above output.

FWIW; you will probably be able to work around this issue by issuing the following command from where you issue your juju commands:
    juju resolved <unit-name/number-of-rabbitmq-server-unit>

In the mean time we will investigate how the install hook of this charm can be made more resilient to this situation.