u_boot_pylib: Allow control of capturing

Tests often capture output so they can check it. This means that if the
test fails it is not easy to see what the output actually was.

Add a -N flag which writes out the output after it has been captured.
This is not a perfect solution but it is simple and seems to work well
in practice.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/u_boot_pylib/terminal.py

@@ -28,6 +28,13 @@ last_print_len = None
 # stackoverflow.com/questions/14693701/how-can-i-remove-the-ansi-escape-sequences-from-a-string-in-python
 ansi_escape = re.compile(r'\x1b(?:[@-Z\\-_]|\[[0-?]*[ -/]*[@-~])')
 
+# True if we are capturing console output
+CAPTURING = False
+
+# Set this to False to disable output-capturing globally
+USE_CAPTURE = True
+
+
 class PrintLine:
     """A line of text output
 
@@ -280,10 +287,17 @@ class Color(object):
 #   ...do something...
 @contextmanager
 def capture():
+    global CAPTURING
+
     capture_out, capture_err = StringIO(), StringIO()
     old_out, old_err = sys.stdout, sys.stderr
     try:
+        CAPTURING = True
         sys.stdout, sys.stderr = capture_out, capture_err
         yield capture_out, capture_err
     finally:
         sys.stdout, sys.stderr = old_out, old_err
+        CAPTURING = False
+        if not USE_CAPTURE:
+            sys.stdout.write(capture_out.getvalue())
+            sys.stderr.write(capture_err.getvalue())