Various fixes:
    
    - Do not require xfsprogs/xfsprogs-devel for el6
    - Require gperftools-devel for non-ppc*/s390* architectures only
    - Do not require junit -- no need to build libcephfs-test.jar
    - Build without libxfs for el6
    - Build without tcmalloc for ppc*/s390* architectures
    - Location of mkcephfs must depend on a rhel release
    - Use epoch in the Requires fields [1130700]