Added base classes for Load Tests and profiler

* added nailgun profiler
* added base clases for load test
* added integration tests

Tests are run only when teh are set in settings
(PERFORMANCE_PROFILING_TESTS) is set on True, also profiler runs
only when this variable is set. All artifacts from profiler are
writen in /tmp/nailgun_load_tests/results/, directory can be
changed in settings.yaml.

DocImpact
Change-Id: I2be46c2a0a51544b12a1d9f2a840d4edc3ede2c4
Blueprint: 100-nodes-support
Merge "Added base classes for Load Tests and profiler"