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.
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.

Why we need dev_loss_tmo here:
   The way in which explicit path mapping is currently implemented requires
   dev_loss_tmo to be a finite value as close to 0 as possible.

   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, it is far more likely that devices
   linger around, are not accessible when a map is initially added (violate a),
   and multipathd does not receive an event for when they become accessible
   (like when they newly appear in case b). This leads to cases in which a
   multipathed root device or SRs are backed by less paths then available.

   The use of dev_loss_tmo 30 generally minimises this problem.

Why this commit, using dev_loss_tmo 30 alone, does not resolve all cases:
    In Trunk a LVHDo*SR pbd-plug or pbd-unplug with multipath enabled will cause
    a multipathd reconfigure. During reconfigure all(!) maps are deleted and
    re-created.
    In conjunction with dev_loss_tmo infinity this makes multipathd forget
    paths forever that are temporaily down when pbd-plug or pbd-unplug are
    called. Multipathd re-creates maps without failed paths, and neither a) nor
    b) are ever triggered. If dev_loss_tmo 30 is used, we get at least away in
    cases pathes are down for more than 30s.
    Even with dev_loss_tmo the bahviour is still signficantly regressed
    compared to past releases. The risk of forgetting good paths is multiplied
    by the amount of SRs attached to a host.

    -> The seperate CA-135899 will serve to follow up on this. <-

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 as outlined in
CA-135899.

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