Update to newer Centos7 images as announced at [1].
Changes included:
* update to GA image
* respect TMP_DIR for image working directory
* use suffix-match rather than prefix-match to build RAW_IMAGE name
to be more robust against weird names
* partition layout work-arounds not needed any-more, all one
partition.
Resulting image booted locally with kvm and virtualbox (after
conversion to vdi)
[1] https://www.redhat.com/archives/rdo-list/2014-August/msg00045.html
Closes-Bug: #1363146
Change-Id: Ie24033468b78587ea87188ee1b843b26895798ff
Initial support for a centos7 image.
This is separate to rhel7 because the major differences are things
like repo and image locations, which are always going to be different.
We should merge any real changes into the redhat-common layers.
Apart from the added support files in centos7/*, the other change is
mostly modifications to redhat-common's extract-image to handle
different partition layouts of the centos7 image.
Change-Id: I943abe5ff0a803f36eda266a79af0d9220edcae7
