test: Add a simple script to run tests on sandbox

A common check before sending patches is to run all available tests on
sandbox. But everytime I do this I have to look up the README. This presents
quite a barrier to actually doing this.

Add a shell script to help. To run the tests, type:

   test/run

in the U-Boot directory, which should be easy to remember.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Teddy Reed <teddy.reed@gmail.com>

test/README

@@ -5,6 +5,17 @@ U-Boot has a large amount of code. This file describes how this code is
 tested and what tests you should write when adding a new feature.
 
 
+Running tests
+-------------
+
+To run most tests on sandbox, type this:
+
+    test/run
+
+in the U-Boot directory. Note that only the pytest suite is run using this
+comment.
+
+
 Sandbox
 -------
 U-Boot can be built as a user-space application (e.g. for Linux). This

test/run

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+# Run all tests
+./test/py/test.py --bd sandbox --build