Add more man pages.
    
    A few man pages were already in place.  This patch uses the --help
    output from each executable to seed a man page for the rest of the
    executables, which include:
    
      - glance
      - glance-cache-cleaner
      - glance-cache-manage
      - glance-cache-prefetcher
      - glance-cache-pruner
      - glance-cache-queue-image
      - glance-control
      - glance-scrubber
    
    Fixes bug 911291.
    
    Change-Id: Ie0de990ff6617e7eb953f270a089c99bc340b4fe