Allow list-backups & status command for inactive/disabled servers

[DavidBoone]

Fixes https://github.com/EnterpriseDB/barman/issues/227

[didiermichel]

Hi @DavidBoone and thank you for your contribution. The original Issue was closed. We will need to either reopen it or create a new issue and discuss it before doing any changes. Notice that PG9.5 is not supported anymore (since 3.3.0).