Ensure that lun_id is an int

The map_vol_to_host function was treating the lun number
as a string rather than an int.  This was causing attempts
to mount storwize_svc volumes to Hyper-V nodes to fail as they
were checking an integer type against a unicode type which
would fail.

This change casts result_lun to an integer after the value has
gone through the ssh injection attack check.  This way Hyper-V
is able to verify if the found LUN is the target LUN, enabling
mount of storwize_svc volumes to Hyper-V.

Change-Id: I96d179f2a58e5948c8ba6c9ae618daad7b8d4c86
Closes-bug: 1269915
Merge "Ensure that lun_id is an int"