Create new expected_warnings helper and some cleanup

Add new helper function for expected warnings during test

Indentation cleanups and avoid skipping doctests if possible.

skimage/measure/_ccomp.pyx

@@ -416,12 +416,12 @@ def label(input, neighbors=None, background=None, return_num=False,
      [0 1 0]
      [0 0 1]]
     >>> from skimage.measure import label
-    >>> print(label(x, neighbors=4))  # doctest: +SKIP
+    >>> print(label(x, connectivity=1)) 
     [[0 1 1]
      [2 3 1]
      [2 2 4]]
 
-    >>> print(label(x, neighbors=8))  # doctest: +SKIP
+    >>> print(label(x, connectivity=2))
     [[0 1 1]
      [1 0 1]
      [1 1 0]]