bitbake: toaster: Add performance testing script

bitbake: toaster: Add performance testing script

This is implemented as a django management command.
For the moment the 'manage.py perf' command will track the toaster
'gui' urls http response code and load time.

To use it:
1. do your toaster builds
2. ensure toaster is started
1. cd bitbake/lib/toaster
2. ln -s ../../../build/toaster.sqlite
3. ./manage.py perf

(Bitbake rev: 4a1fc6851d21500150715f0e8fa03c0b228ec5f2)

Signed-off-by: Ionut Chisanovici <ionutx.chisanovici@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>