engine_page: catch exception from vdscli.connect()

After the node installation and before the registration
there are no .pem files in /etc/pki/vdsm/certs so
vdscli.connect() will raise an exception when users
login as admin to TUI access. This patch catches and log
the exception.

Change-Id: I5a0333837a3aec2364362728951b1623b46065a0
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1100226
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>