Fix Ctrl-Alt-Del confirmation in noVNC

This removes the Ctrl-Alt-Del button from the power class (where the
previous, broken confirmation dialog box was from) and puts a different
confirmation box in the noVNC.js file.

The power class javascript did nothing for the Ctrl-Alt-Del button,
since the javascript in novnc.html is what sends the Ctrl-Alt-Del.
Therefore, the dialog must go in novnc.html or the Ctrl-Alt-Del send
must be moved out of novnc.html.

References #16377
Fix typo/minor grammar issue

Fix a typo in the Configuring docs and finish an unfinished sentence
explaining GWM's groups feature.
Update Vagrant docs with proper location

Change the location of the venv to /opt/ganeti_webmgr/ and explain the
difference between the Apache server (running by default) and the
development server.
Add init.d script for vncauthproxy

Add Centos and Ubuntu init scripts as well as documentation
detailing how to install them.
Revert "Add init.d script for vncauthproxy"

This reverts commit 992de9f35930eb95303451dedd82b90d535c7144.
Pushed to the wrong branch.
Revert "Revert "Add init.d script for vncauthproxy""

This reverts commit bd6c007b88374774a8e24c47336cc55e6c6238b7.
Commit to the correct branch this time, adding init.d script for
vncauthproxy. This includes the documentation needed to set it up
on Centos and Debian/Ubuntu systems.