mgmt_server: fix node_list/1 if no mgmt_server is configured
mgmt_server: fix node_list/1 if no mgmt_server is configured

(regression in r4559)
seyyed/scalaris,digshock/scalaris,tectronics/scalaris,digshock/scalaris,tectronics/scalaris,seyyed/scalaris,tectronics/scalaris,tectronics/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris,tectronics/scalaris,seyyed/scalaris,digshock/scalaris,digshock/scalaris,seyyed/scalaris,digshock/scalaris,seyyed/scalaris,digshock/scalaris,seyyed/scalaris,tectronics/scalaris