3.3.3. Create the SQLite Database needs a step to add a var directory

[vrracing]

If you don't create xblock_development/var the command

python xblock-sdk/manage.py migrate

will fail.

I found this solution by François Bouchet here...

https://groups.google.com/forum/#!searchin/edx-code/python$20xblock-sdk$2Fmanage.py$20migrate%7Csort:date/edx-code/PAru0A1k3No/IfFXAu80AQAJ