tests/vm: Allow to set qemu-img path

By default VM build test use qemu-img from system's PATH to
create the image disk. Due the lack of qemu-img on the system
or the desire to simply use a version built with QEMU, it would
be nice to allow one to set its path. So this patch makes that
possible by reading the path to qemu-img from QEMU_IMG if set,
otherwise it fallback to default behavior.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20191114134246.12073-2-wainersm@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

tests/vm/basevm.py

@@ -152,6 +152,11 @@ class BaseVM(object):
     def build_image(self, img):
         raise NotImplementedError
 
+    def exec_qemu_img(self, *args):
+        cmd = [os.environ.get("QEMU_IMG", "qemu-img")]
+        cmd.extend(list(args))
+        subprocess.check_call(cmd)
+
     def add_source_dir(self, src_dir):
         name = "data-" + hashlib.sha1(src_dir.encode("utf-8")).hexdigest()[:5]
         tarfile = os.path.join(self._tmpdir, name + ".tar")