webadmin: Using stored VDS.sshUsername instead of default root in reinstall
view

When loading InstallHost model we launched InstallPopupView filled with
root username in the ssh user name area. This patch uses the stored VDS
object and places in the username field the SshUsername that was saved during
first installation.

Change-Id: Ia9870d35f7dbabb102a809d02c356c15dd1bebff
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>