We'll aggregate testing of all cache modes in this test later on.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

The disk cache mode translates to various frontend and backend
attributes for the qemu block layer. For the frontend device the
'writeback' parameter is used and provided as 'write-cache'. Implement
this so that we can later switch to using -blockdev where we will not
pass the cachemode directly any more.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>

Prepare the tests for adding the new parameter. The parameter was
introduced in qemu-2.7.0, so add a forked version of the test case to
see that it is formatted properly.

This test is also an example how the new testing macros should be used.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>