Add test to verify that CLI examples only contain ascii

[jamesls]

As part of this change I also fixed all the examples that failed
as a result of this test being added (#1873).

Also gives decent failure messages:

======================================================================
FAIL: tests.functional.docs.test_examples.test_all_examples_have_only_ascii('aws-cli/awscli/examples/autoscaling/describe-tags.rst',)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ".virtualenvs/aws-cli/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "aws-cli/tests/functional/docs/test_examples.py", line 84, in verify_has_only_ascii_chars
    "\n\n%s\n" % (filename, line_number, error_text))
AssertionError: Non ascii characters found in the examples file aws-cli/awscli/examples/autoscaling/describe-tags.rst, line 53:

-auto-scaling-group —-starting-token Z
                    ^

cc @kyleknap @JordonPhillips

[JordonPhillips]

⛵ This is what I get for staging my sed command in Notes