LUCENE-4949: Make the version prefix (SNAPSHOT) separately configurable to enable Jenkins use its BUILD_ID variable, cleanup code duplication (merged from branch_4x r1470978)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_3@1483404 13f79535-47bb-0310-9956-ffa450edef68