Add rally performance gate job for glance

This patch is init setup of rally gate job.
After merging this everybody will be able to change
rally-scenarios/glance.yaml to run any benchmarks with any load in gates.

Change-Id: Ic5e58856ece15e4d130ccd1e0057917441b01728
Use safe way through "with" statement to work with files

It's unsafe to just open and write to file. Cause if something went wrong
during writing to file we won't close fd.

Change-Id: I924b8962b3e0c936f3a20260844178783feaf544
Merge "Add rally performance gate job for glance"