Watch mode breaks on accented characters

[brobsc]

Reproduction:

1. Log in to tst
2. Run easy_tst watch
3. Copy an apparent (4 chars) checkout code that contains an invalid ascii character

Traceback (most recent call last):
  File "/usr/local/bin/easy_tst", line 6, in <module>
    exec(compile(open(__file__).read(), __file__, 'exec'))
  File "/Users/bruno/easy_tst/bin/easy_tst", line 26, in <module>
    easy_clipboard.watch_mode()
  File "/Users/bruno/easy_tst/easy_tst/easy_clipboard.py", line 37, in watch_mode
    print('Trying to checkout: "{}"'.format(cv))
UnicodeEncodeError: 'ascii' codec can't encode character u'\xc1' in position 0: ordinal not in range(128)

[brobsc]

Also breaks when clipboard content is longer than 4 characters.

Starting watch mode.
Traceback (most recent call last):
  File "/usr/local/bin/easy_tst", line 6, in <module>
    exec(compile(open(__file__).read(), __file__, 'exec'))
  File "/Users/bruno/easy_tst/bin/easy_tst", line 22, in <module>
    easy_clipboard.watch_mode()
  File "/Users/bruno/easy_tst/easy_tst/easy_clipboard.py", line 43, in watch_mode
    print('Trying to checkout: "{}"'.format(cv))
UnicodeEncodeError: 'ascii' codec can't encode characters in position 88-89: ordinal not in range(128)

[brobsc]

Tracked on #10 now.