Adds the file api/bots_api/provision.py that installs dependencies
for bots using pip. This file is also used by run.py when running
a bot. However, for testing, you need to separately provision the bots.
Since few bots directly call 'send_message' function of
'BotHandlerApi' class instead of calling 'send_reply' function
first, add 'mock_test_send_message' to check for 'send_message'
function.
All test_<bot>.py files now need to specify which function the bot
will be sending the response to, for each particular message.
Make 'test_virtual_fs.py' and 'test_thesaurus.py' test files
consistent with other bots.
