CA-125717: Specify dev_loss_tmo in /etc/multipath.conf

Since implementing CA-108915 we need to specify dev_loss_tmo in
/etc/multipath.conf to properly handle timed out devices.
It seems that the setting accidently got lost in a merge, when porting the
configuration file from guest-packages.hg to dm-multipath.git. This commit
reinstates the dev_loss_tmo setting that we had before.

Signed-off-by: Robert Breker <robert.breker@citrix.com>