Add rally element

Add an element installing Rally. Rally is a tool for benchmarking
and profiling OpenStack installations. It can be useful for detection
of bottlenecks and debugging performance issues in deployed clouds.

Change-Id: Ib8b5b937d19a59610da375b1a8256fd5a412c223
Install libffi-dev in heat element

Heat added glanceclient as a requirement, and glanceclient can't
be installed without libffi-dev installed.

Change-Id: I34b50c2b1ec4322c511d3a3677cfd3424a40d1c8
Closes-Bug: #1317998
Merge "Install libffi-dev in heat element"
Merge "Add rally element"