OEcore/bitbake are moving to use the clearer ":" as an overrides
separator.

This is pass one of updating the meta-virt recipes to use that
syntax.

This has only been minimally build/runtime tested, more changes
will be required for missed overrides, or incorrect conversions

Note: A recent bitbake is required:

    commit 75fad23fc06c008a03414a1fc288a8614c6af9ca
    Author: Richard Purdie <richard.purdie@linuxfoundation.org>
    Date:   Sun Jul 18 12:59:15 2021 +0100

        bitbake: data_smart/parse: Allow ':' characters in variable/function names

        It is becomming increasingly clear we need to find a way to show what
        is/is not an override in our syntax. We need to do this in a way which
        is clear to users, readable and in a way we can transition to.

        The most effective way I've found to this is to use the ":" charater
        to directly replace "_" where an override is being specified. This
        includes "append", "prepend" and "remove" which are effectively special
        override directives.

        This patch simply adds the character to the parser so bitbake accepts
        the value but maps it back to "_" internally so there is no behaviour
        change.

        This change is simple enough it could potentially be backported to older
        version of bitbake meaning layers using the new syntax/markup could
        work with older releases. Even if other no other changes are accepted
        at this time and we don't backport, it does set us on a path where at
        some point in future we could
        require a more explict syntax.

        I've tested this patch by converting oe-core/meta-yocto to the new
        syntax for overrides (9000+ changes) and then seeing that builds
        continue to work with this patch.

        (Bitbake rev: 0dbbb4547cb2570d2ce607e9a53459df3c0ac284)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

As part of allowing different types of oci images to be created,
we split our IMG_cmd into .inc files that can then be specific to
the selected type.

For the umoci backend: We can take the same options as sloci
expects and use umoci to create images.

The resulting OCI image is similar, but by using umoci, we set
the stage to do multi-tag, or multi-layer images in the future.

But for now, we are functionally equivalent to the sloci backend.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>