engine: Code cleanup for device refresh treatment

Performed some clean ups in VdsUpdateRunTimeInfo code which treats
devices refreshment, to make code easier to read and understand:

1. Don't use toString() on objects sent to log.xxxFormat() method since
     this is what happens anyway.
2. Moved lines of code closer to where they're really needed.
3. Used Set instead of HashSet in reference declaration.
4. Inlined some variables that were used only in one place.
5. Used Entities.businessEntitiesById() method instead of manual map
     building.
6. Used StringUtils.defaultString(xxx) instead of variations of
     StringUtils.defaultIfEmpty(xxx, "").
7. Changed code to "fail early" instead of nesting (5 levels of nesting
     is excessive).
8. Reordered conditions so that positive case is first.
9. General formatting (removed unecessary line breaks, added some where
   needed).

Change-Id: I978b46912f095d636ea0c4f1c58d3bb14083d855
Bug-Url: https://bugzilla.redhat.com/872165
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>