Add graphite graph of gate failure rates to e-r page

In addition to knowing how frequently a bug is hit, we also want to know
the overall failure rates.

Since this graph is more dense then the others on the page, make it a
twice as tall at 600x400

Change-Id: I8e6a5e8d45e8d57c8128eefe0efeecc8255b2497
Merge "Add graphite graph of gate failure rates to e-r page"