fix config name used to detect public url (#1923)
fix config name used to detect public url (#1923)

it was using env var name instead of setting name

SDCP-235
petrjasek/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core,petrjasek/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,superdesk/superdesk-core,petrjasek/superdesk-core