test: Add a function to restart U-Boot

Add a proper function for this rather than using internal functions. Use it
in the single call site.

Also, do a restart at the end of the vboot test to reset to the normal
device tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Stephen Warren <swarren@nvidia.com>

test/py/tests/test_vboot.py

@@ -65,8 +65,7 @@ def test_vboot(u_boot_console):
             sha_algo: Either 'sha1' or 'sha256', to select the algorithm to
                     use.
         """
-        cons.cleanup_spawn()
-        cons.ensure_spawned()
+        cons.restart_uboot()
         with cons.log.section('Verified boot %s %s' % (sha_algo, test_type)):
             output = cons.run_command_list(
                 ['sb load hostfs - 100 %stest.fit' % tmpdir,
@@ -190,4 +189,6 @@ def test_vboot(u_boot_console):
         test_with_algo('sha1')
         test_with_algo('sha256')
     finally:
+        # Go back to the original U-Boot with the correct dtb.
         cons.config.dtb = old_dtb
+        cons.restart_uboot()

test/py/u_boot_console_base.py

@@ -393,6 +393,11 @@ class ConsoleBase(object):
             pass
         self.p = None
 
+    def restart_uboot(self):
+        """Shut down and restart U-Boot."""
+        self.cleanup_spawn()
+        self.ensure_spawned()
+
     def get_spawn_output(self):
         """Return the start-up output from U-Boot