Ensure that lun_id is an int for NetApp Drivers

Various NetApp drivers were treating the lun_id as a string
rather than an int.  This was causing attempts to mount NetApp
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
mounting of NetApp volumes to Hyper-V.

This change also refactors initialize_connection into some helper
methods so as to enable simpler unit testing of the patchset.

Closes-bug: 1372808

Change-Id: I308b3b2dff315ec33451fb45a30ecd53d5d4c353
(cherry picked from commit:2d0204ff3ca3a7d42fac5722d577e18edd34ea83)
Merge "Ensure that lun_id is an int for NetApp Drivers" into stable/juno