Show a pretty progressbar when uploading and downloading an image.

Add a new module that contain generic wrapper for file and iterator, which
are used to wrap image to upload and the request body iterator in upload and
download cases repectively, to show and advance a pretty progress bar when this
laters are consumed, The progress bar is triggered by adding a --progress command
line argument to commands: image-create, image-download or image-update.

Change-Id: I2ba42fd0c58f4fa087adb568ec3f08246cae3759
bug fix: LP#1112309
blueprint: progressbar-when-uploading

tests/utils.py

@@ -33,8 +33,9 @@ class FakeAPI(object):
 
     def raw_request(self, *args, **kwargs):
         fixture = self._request(*args, **kwargs)
-        body_iter = http.ResponseBodyIterator(StringIO.StringIO(fixture[1]))
-        return FakeResponse(fixture[0]), body_iter
+        resp = FakeResponse(fixture[0], StringIO.StringIO(fixture[1]))
+        body_iter = http.ResponseBodyIterator(resp)
+        return resp, body_iter
 
     def json_request(self, *args, **kwargs):
         fixture = self._request(*args, **kwargs)
@@ -95,3 +96,17 @@ class TestResponse(requests.Response):
     @property
     def text(self):
         return self._text
+
+
+class FakeTTYStdout(StringIO.StringIO):
+    """A Fake stdout that try to emulate a TTY device as much as possible."""
+
+    def isatty(self):
+        return True
+
+    def write(self, data):
+        # When a CR (carriage return) is found reset file.
+        if data.startswith('\r'):
+            self.seek(0)
+            data = data[1:]
+        return StringIO.StringIO.write(self, data)