Add some rally scenarios

This change adds configuration directory for rally.

Implements blueprint rally-gate-check

Change-Id: I49ed3025bb90355b851526af9b5a469c7c84fdc9
Standardize timestamp fields of ceilometer API

For currently, the timestamp in query fields is not unified, this
patch standardizes the usage of timestamp query fileds:

- unify the time query filed in API to *timestamp* supported only.
- unify the time related fileds of filters to start_timestamp and
  end_timestamp to simplify the process logic.
- improve the _query_to_kwargs method to give explicit presentation
  if user specifies unsupported query fields.

Change-Id: Ic3ade312efa89edd01d2ee5ae31d341805b11f79
Closes-bug: #1295104
Closes-bug: #1291171
Add docs about volume/snapshot measurements

This change allows to add information about
measurements of volumes/snapshots.

Implements: blueprint add-new-notifications-types-for-volumes-and-snapshots
Change-Id: I23ec262dc4617af7c270ffc1a4dd17ad9ac69841
Make compute discovery pollster-based, not agent-level

Partially-Implements-Blueprint: merge-compute-central-agents

Change-Id: I02c9a12b0fcd55a7d59688853f3c08e505b4bf3f
Modify tests to support ordering of wsme types

When PYTHONHASHSEED is enabled the ordering of the wsme types are changed.
This fails the tests that take the type order into account when an assertEqual
is checked on the error message. The assertEqual is now changed to an
assertIn where the ordering of the types do not matter.

Change-Id: I0f445013802273478f5f448fa0350b9a1b140414
Closes-bug: #1399631
Merge "Add docs about volume/snapshot measurements"
Merge "Standardize timestamp fields of ceilometer API"
Merge "Make compute discovery pollster-based, not agent-level"
Improve links in config docs

Currently duplication part from configuration.rst file was removed
(patch https://review.openstack.org/#/c/133035) but links in events.rst are
still refering to removed part of docs.

This patch improves links.

Closes-bug: #1401444
Change-Id: I99037f99f3fcb40eb27b56e1581bf60f32ff3051
Merge "Modify tests to support ordering of wsme types"
Merge "Add some rally scenarios"
Merge "Improve links in config docs"