Allow qemu access to modify backing files in case when we want to delete
a checkpoint.

This patch adds tracking of which images need to be relabelled when
calculating the transaction, the code to relabel them and rollback.

To verify that stuff works we also output the list of images to relabel
into the test case output files in qemublocktest.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

Use the synthetic test data to verify that the algorithm correctly picks
bitmaps to merge when the bitmap is changed along with the image itself.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

Add test cases for merging various pairs of bitmaps when snapshots were
created together with checkpoints.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

Add all intermediate steps and deletion of the current checkpoint on a
flat (single-image) disk image.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

Add test infrastructure and a basic test for bitmap deletion.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>