Ticket 48965 - Fix generation of the pre-release version
    
    Description: Previously, when building DS from git checkout, pre-release
    version didn't contain git commit id, though supporting code existed.
    
    Fix description: Generate pre-release version according to Fedora Naming
    Guidelines for snapshot packages [1]:
    - change date format to YYYYMMDD
    - remove '-' since it's not allowed
    
    https://fedorahosted.org/389/ticket/48965
    
    Reviewed by: mreynolds@redhat.com (Thanks!)
    
    [1] https://fedoraproject.org/wiki/Packaging:Naming?rd=Packaging:NamingGuidelines#Snapshot_packages