Enable overrides passing to OZ (memory, cpus, default image)
 which now allows qcow2 to be default image type

* imagefactory
    - qcow2 is now the default output vs raw
    - corrected the parsing of images, streamlined
    - created ImageFunctions class that that enable
      passing of oz override metadata in json
    - by default, we now require:
        - memory > 2047
        - cpus = 2
        - default_image = qcow2

* taskbase
    * minor cleanup to expose the name-release
installer.py Allow the output dir to be used from the configuration file
    and not require -o to run by default

    - Fix bug where output from config.ini was not being passed in
      and used.
taskbase: Deal with rpmostree_cache_dir not being set
taskbase: Infer configdir from path to config file

This should allow having an outputdir-independent config.ini in git.
Make --config argument required again

The new model is:
1) config.ini is kept in git, and does not include output directory
2) You have to specify it on the command line
3) outputdir defaults to $(pwd)

As part of this, move common handling of -c argument to taskbase.
taskbase: Default outputdir to process cwd again

I was getting ostree_repo=/repo because outputdir was "", and not
noticing, and being very, very confused.
Remove unnecessary import
treecompose: Add --check passwd/groups, needs latest rpm-ostree
treecompose: Don't traceback if rpm-ostree command fails