Fix make_test_data tools script

Method get_connection has been renamed to
get_connection_from_config.

Resource is object not dictionary, so attributes needs to be
accessed that way.

Change-Id: I19e09f3e9077d3346b4361fa6975a3e696e2e765
Related-Bug: #1349791
Extracting make_resource_metadata method

Dividing this method into multiple helps to reuse it in
some tools scripts for generating data.

Change-Id: I45230cd43d82e946fab394c4b6a1fe6b64cd8937
Related-Bug: #1349791
Enhancing the make_test_data script

-Adding random boundaries rather than exact value for samples
-Allowing to pass datetime object or string
-Extracting make_test_data func, so it can be imported elsewhere
-Converting the integer time span to datetime

Change-Id: Iffbc8d9711b2f301a1f28b49980691ab34d17c20
Related-Bug: #1349791
Add data generators.

+ Sample generator. It uses pika+rabbitmq and create samples with unconfigurable data.
+ Make test data. Written by Ladislav Smola generator. It writes configurable samples with
record_metering_data of backend.
+ Send sample messages. It uses make tests data for create samples and send it with oslo messaging.
Merge branch 'master' of https://github.com/ityaptin/ceilometer into performance-tests