Core: add unit test case for FedMsgContext.send_message
Core: add unit test case for FedMsgContext.send_message

it tests that send_message()
- deprecation warning is properly displayed
- it calls publish() with correct arguments

vivekanand1101/fedmsg,cicku/fedmsg,chaiku/fedmsg,maxamillion/fedmsg,mathstuf/fedmsg,fedora-infra/fedmsg,fedora-infra/fedmsg,maxamillion/fedmsg,fedora-infra/fedmsg,chaiku/fedmsg,cicku/fedmsg,chaiku/fedmsg,vivekanand1101/fedmsg,cicku/fedmsg,vivekanand1101/fedmsg,mathstuf/fedmsg,pombredanne/fedmsg,mathstuf/fedmsg,maxamillion/fedmsg,pombredanne/fedmsg,pombredanne/fedmsg