Make caching more tolerant of failures

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Touch the cache directories when we have a cache hit

This will help with GCing the cache

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Make the RPM cache dir configurable

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Set the RPM cache dir for the build system

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>
Merge pull request #79 from jonludlam/cache-fixes

Cache fixes