Fix error when trying to edit the editable parts of an imported ssh host with a user name/key.
In the reported bug, changing the profile associated with an autoimported entry fails because the user name is populated and so is the use sshconfig checkbox. There were a few ways to fix this, but I simply skip the test if the username field is disabled. This leads to another issue: The state of the imported flag is not carried through, so then the entry loses its imported status. This patch also fixes that by, again, observing the enable state of the user name field and using it to populate the to-be-saved data item's imported flag.