The updater need reset the internal state when finish with error

This is needed to allow the next update request to work.

This was missed in the last patch "Show a error message
if the activity updater can't connect to the server"

Signed-off-by: Gonzalo Odiard <godiard@sugarlabs.org>
Fix #4733 - remove warning on username change

If the user changes the username on My Setting -> About me view and then
reverts it to the initial username, remove the warning about restart.
Manage restart message on reverting to initial username

Take into consideration also the following usecases:
 - user also changes the color
 - user cancels the modifications and reverts to the initial username
 - user makes a change, reverts, clicks accept, reenters the About Me settings