Fig bug in split_buffer where input was being discarded

Also, write some tests for it.

fig/cli/utils.py

@@ -83,3 +83,28 @@ def mkdir(path, permissions=0o700):
 
 def docker_url():
     return os.environ.get('DOCKER_HOST')
+
+
+def split_buffer(reader, separator):
+    """
+    Given a generator which yields strings and a separator string,
+    joins all input, splits on the separator and yields each chunk.
+
+    Unlike string.split(), each chunk includes the trailing
+    separator, except for the last one if none was found on the end
+    of the input.
+    """
+    buffered = str('')
+    separator = str(separator)
+
+    for data in reader:
+        buffered += data
+        while True:
+            index = buffered.find(separator)
+            if index == -1:
+                break
+            yield buffered[:index+1]
+            buffered = buffered[index+1:]
+
+    if len(buffered) > 0:
+        yield buffered