Provide same info as 'pveversion -v' on GUI.

We want to be able to diplay that information on the GUI.

Used to display additional information to the user (reboot required? database
up to date? ...)

The requirement to have VM.Allocate it non-obvious and confusing
if the VM already exists. If the user can backup, he should also be able
to restore that backup.

System upgrade almost always requires user input.

code cleanups

apt-get uses similar code.

And log a message to syslog when we update the package list.

To re-open database - else we get old/cached entries.

Fetching changelog at server side avoids security problems at
client (Same-Origin-Policy).

And avoid to use debian version, because that changes over time and
it is clumsy to keep in sync.

Signed-off-by: Stefan Priebe <s.priebe@profihost.ag>