VistATaskmanUtil: Handle Multiple Volume Set

in verifyTaskmanSiteParameter method, enhance to handle
the sitution that there are multiple volume set in a VistA
instance.

Also refactoring findChoiceNumber in VistAPackageInfoFetcher.py
to handle simple choice selection.

OSEHRA-Id: http://issues.osehra.org/browse/VAF-80
Change-Id: Iaa0da640459bcb6fac01a4b3a70534f3c4952d42
Merge "VistATaskmanUtil: Handle Multiple Volume Set"