Why is Steam not able to connect Steam-Network?
Same problem on German Ubuntu forum
http://forum.ubuntuusers.de/topic/steam-verbindet-nicht-zum-server/
This command helped me too
steam --reset
Removing appcache helped me till a new steam version was released which seems to have it fixed.
You can remove appcache via terminal
rm -Rf ~/.steam/steam/appcache
Don't do this with sudo.
I have been able to reproduce this with perfect network connectivity when steam is closed unexpectedly. The solution in my case was to remove:
.local/share/Steam/config
This solution worked for me, and didn't force me to reinstall any game, just to login again