Separate snapshot tag var names from original

 - original tag variables in pom.xmls are being used also outside
   of the poms (namely, in Dockerfiles) and the new tag usage is not
   taken in use in all images yet, so the tag names are now
   differentiated to support old usage where necessary
 - add STAGING-latest tag in TagSnapshotVersion groovy script as a
   quick fix for odlsli-alpine dependencies for now
 - minor typo corrections
Issue-ID: CCSDK-3019
Signed-off-by: Lasse Kaihlavirta <l.kaihlavirt@partner.samsung.com>
Change-Id: Ib6b5e275ea305f5871f124da78a6e94b126c0266