Trivial update to parameters for _instance_update

Change-Id: I23d2c17ff3c54be97a2710da316eaa4f06cc9425
Merge branch 'havana/1.4' into havana/1.5-merge

The fixed being merged was already included in havana/1.5
and this is a trivial sync-up merge.

Change-Id: I1b1a40c88f289273aa663219bf58d0e71134efd8
Trival fix up for a bad merge that caused discard to be called twice.

Change-Id: I8c6bb5aaa2a25f2dc2fad94813f867866aabb138
Ensure only desired fields are updated during _instance_update(...)

OS-279

The method _instance_update now clears out any local modifications
that may have been made to the instance object before updating/saving
it. This prevents unwanted updates occuring to the database.

This problem was revealed when the instance's host attribute is
temporarily changed during migration. This change is noted in the
object, and during the instance update the host attribute also
get updated. This was an unintended side-effect.

Change-Id: Ibaea13f9d131261ad4882395de76ea3c14df9988
Merge branch 'havana/1.5' into icehouse/1.5

Change-Id: I60fcb018800f7859bed3506beb86eb58add3c202