Fix NPE while parsing response on getting conference info

[herasymchuk]

This is to fix behavior described at: https://community.jitsi.org/t/jitsi-reservation-system-conflict-workflow/20548 When reservation API returns HTTP 409, Jicofo fetches info about conflicting conference and NPE occurs on parsing response from GET /conference

[jitsi-jenkins]

Hi, thanks for your contribution! If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[bgrozev]

The reservation system was moved to a prosody module.