- redo mock.util.do() to use python subprocess module, which should be much
        more maintainable than our old homegrown code.
    - Fix exclude= lines once again. Yum fnmatch parser doesnt understand [!x]
        notation
    - add --unpriv and --cwd options to run chroot commands without elevated
        privs and in a specific working directory (under the root).
    - mount all filesystems when running chroot commands
    - remove redundant ccache init since we now source /etc/profile.d/ccache.sh