test/py: Implement pytest infrastructure

This tool aims to test U-Boot by executing U-Boot shell commands using the
console interface. A single top-level script exists to execute or attach
to the U-Boot console, run the entire script of tests against it, and
summarize the results. Advantages of this approach are:

- Testing is performed in the same way a user or script would interact
  with U-Boot; there can be no disconnect.
- There is no need to write or embed test-related code into U-Boot itself.
  It is asserted that writing test-related code in Python is simpler and
  more flexible that writing it all in C.
- It is reasonably simple to interact with U-Boot in this way.

A few simple tests are provided as examples. Soon, we should convert as
many as possible of the other tests in test/* and test/cmd_ut.c too.

The hook scripts, relay control utilities, and udev rules I use for my
own HW setup are published at https://github.com/swarren/uboot-test-hooks.

See README.md for more details!

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org> #v3

test/py/multiplexed_log.css

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2015 Stephen Warren
+ * Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ */
+
+/*
+ * This provides pretty formatting of the HTML log file, e.g.
+ * - colored bars beside/above log sections for easily parsed delineation.
+ * - color highlighting of various messages.
+ */
+
+body {
+    background-color: black;
+    color: #ffffff;
+}
+
+pre {
+    margin-top: 0px;
+    margin-bottom: 0px;
+}
+
+.implicit {
+    color: #808080;
+}
+
+.section {
+    border-style: solid;
+    border-color: #303030;
+    border-width: 0px 0px 0px 5px;
+    padding-left: 5px
+}
+
+.section-header {
+    background-color: #303030;
+    margin-left: -5px;
+    margin-top: 5px;
+}
+
+.section-trailer {
+    display: none;
+}
+
+.stream {
+    border-style: solid;
+    border-color: #303030;
+    border-width: 0px 0px 0px 5px;
+    padding-left: 5px
+}
+
+.stream-header {
+    background-color: #303030;
+    margin-left: -5px;
+    margin-top: 5px;
+}
+
+.stream-trailer {
+    display: none;
+}
+
+.error {
+    color: #ff0000
+}
+
+.warning {
+    color: #ffff00
+}
+
+.info {
+    color: #808080
+}
+
+.action {
+    color: #8080ff
+}
+
+.status-pass {
+    color: #00ff00
+}
+
+.status-skipped {
+    color: #ffff00
+}
+
+.status-fail {
+    color: #ff0000
+}