block: an interoperability test for luks vs dm-crypt/cryptsetup

It is important that the QEMU luks implementation retains 100%
compatibility with the reference implementation provided by
the combination of the linux kernel dm-crypt module and cryptsetup
userspace tools.

There is a matrix of tests to be performed with different sets
of encryption settings. For each matrix entry, two tests will
be performed. One will create a LUKS image with the cryptsetup
tool and then do I/O with both cryptsetup & qemu-io. The other
will create the image with qemu-img and then again do I/O with
both cryptsetup and qemu-io.

The new I/O test 149 performs interoperability testing between
QEMU and the reference implementation. Such testing inherantly
requires elevated privileges, so to this this the user must have
configured passwordless sudo access. The test will automatically
skip if sudo is not available.

The test has to be run explicitly thus:

    cd tests/qemu-iotests
    ./check -luks 149

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/common

@@ -155,6 +155,7 @@ check options
     -ssh                test ssh
     -nfs                test nfs
     -archipelago        test archipelago
+    -luks               test luks
     -xdiff              graphical mode diff
     -nocache            use O_DIRECT on backing file
     -misalign           misalign memory allocations

tests/qemu-iotests/group

@@ -150,3 +150,4 @@
 145 auto quick
 146 auto quick
 148 rw auto quick
+149 rw auto sudo