Avoid import time side-effect from font_manager

[kitchoi]

Currently importing kiva.fonttools.font_manager has a side effect of loading the system font files. This makes it difficult to configure logging in tests should the side effect emits log messages.

For a project that depends on enable (e.g. via chaco), running a test suite using unittest discover may trigger log messages because FontManager fails to parse one or many system fonts:

[00:03:41] Traceback (most recent call last):
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 1440, in <module>
[00:03:41]     fontManager = pickle_load(_fmcache)
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 1050, in pickle_load
[00:03:41]     fh = open(filename, 'rb')
[00:03:41] FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Users\\appveyor\\AppData\\Roaming\\Enthought\\kiva\\fontList.cache'
[00:03:41] 
[00:03:41] During handling of the above exception, another exception occurred:
[00:03:41] 
[00:03:41] Traceback (most recent call last):
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 738, in createFontList
[00:03:41]     prop = ttfFontProperty(fpath, font)
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 525, in ttfFontProperty
[00:03:41]     name = props[(1, 0, 0, 1)].decode()
[00:03:41] KeyError: (1, 0, 0, 1)
[00:03:41] Could not covert font to FontEntry for file C:\windows\Fonts\LeelawUI.ttf
[00:03:41] Traceback (most recent call last):
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 1440, in <module>
[00:03:41]     fontManager = pickle_load(_fmcache)
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 1050, in pickle_load
[00:03:41]     fh = open(filename, 'rb')
[00:03:41] FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Users\\appveyor\\AppData\\Roaming\\Enthought\\kiva\\fontList.cache'
[00:03:41] 
[00:03:41] During handling of the above exception, another exception occurred:
[00:03:41] 
[00:03:41] Traceback (most recent call last):
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 738, in createFontList
[00:03:41]     prop = ttfFontProperty(fpath, font)
[00:03:41]   File "C:\Users\appveyor\.edm\envs\py36-ci\lib\site-packages\kiva\fonttools\font_manager.py", line 525, in ttfFontProperty
[00:03:41]     name = props[(1, 0, 0, 1)].decode()
[00:03:41] KeyError: (1, 0, 0, 1)
...
(many similar lines for different font files)

Because this happens at import time, it is difficult to silent these messages in the test environment only.