When installing libnice from sources it won't show in the debian package listing. I use Ubuntu 18.04 as well and i removed the libnice packages shipped by Ubuntu and installed libnice from sources:
15:19:29 root@janus5vm ~ # dpkg -l | grep libnice
15:19:38 root@janus5vm ~ # ldconfig -p | grep libnice
212: libnice.so.10 (libc6,x86-64) => /usr/lib/libnice.so.10
213: libnice.so (libc6,x86-64) => /usr/lib/libnice.so
Janus detected the manually installed libs just fine and it is using them. If i inspect the running janus process i can see it:
15:25:54 root@janus5vm ~/janus/janus-gateway # lsof -p 18655 | grep nice
63:janus 18655 root mem REG 8,2 1488680 1327574 /usr/lib/libnice.so.10.9.0