[Ubuntu] Enable hibernation

Ubuntu by default has the hibernation option disabled, even if the system is installed with enough swap space.

Before enabling it, first check if it works without issues by running this command:

sudo pm-hibernate

If the system hibernates correctly and you don't see any errors, edit the /var/lib/polkit-1/localauthority/10-vendor.d/com.ubuntu.desktop.pkla file:

gksu gedit /var/lib/polkit-1/localauthority/10-vendor.d/com.ubuntu.desktop.pkla

Then look for these two sections:

[Disable hibernate by default in upower]
[Disable hibernate by default in logind]

And change the ResultActive value to yes

Save, reboot and you'll have the option to hibernate the system now.