Login screen asks for wifi password on startup

[Jaromir Obr]

Similar to #1270791

Steps I did:
----
# Install Ubuntu desktop from live image (fresh installation)
# Set WiFi connection and enter password - it's saved well. I'm using a hidden network with WPA2-PSK encryption
# Reboot

Expected result:
As the password was saved, no dialog requiring it appears

Actual result:
Always when I get the login screen, the popup window asking for password appears.
Note that when I login, the network connection is established correctly

Workaround: Disable the option "All users may connect to this network" in the wifi connection settings. The dialog with password won't appear (OK), however wifi is not functional in login screen.

Used HW:
laptop HP Envy 13 Skylake (13-d006nc), network adapter Intel Wireless AC-7265, WiFi router Comtrend VR-3026e Multi-DSL

Used SW:
Ubuntu 15.10 x64 desktop (unity)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.