Add base utils for keystone benchmarks

This patch introduce keystone benchmarks with keystone base utils
+ add 2 keystone benchmark scenarios:
1) create_user - just create user one by one
2) create_delete_user - create & delete user

Add tests for utils and benchmarks

Samples included

blueprint keystone-benchmark

Change-Id: I9362135877bb1bc904fc8ed93c74eba89686e78a
Merge "Add base utils for keystone benchmarks"