CA-125717: Reinstate default 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 lost devices devices.
It seems that the setting accidentaly got lost 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.

Background for why we use dev_loss_tmo:
   The way in which explicit path mapping is currently implemented on XenServer
   requires dev_loss_tmo to be a finite value a lot closer to 0 than to
   infinity.

   This is because multipathd will only monitor devices that are:
   a) accessible (scsi_id works) when a new map is initially added
   b) devices that appear after new map is added.
   In case of  dev_loss_tmo infinity, devices can linger around, be not
   accessible when a map is initially added(violate a), and multipathd doesn't
   receive an event for when they become accessible (like when they newly
   appear in case b). This might lead to cases SRs are backed by less paths
   then available.

   The use of dev_loss_tmo 30 minimises the chances of this happening.

Signed-off-by: Robert Breker <robert.breker@citrix.com>
CA-125717: Make NETAPP LUN.* default to dev_loss_tmo 30 as a workaround

As the inbox device specific entry specifies dev_loss_tmo infinity, we need to
customise it in multipath.conf until we overcome the limitations when combining
explicit path mapping with larger values for dev_loss_tmo.

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