Refactor test framework

Manila's test framework is pretty old and requires update.

Changes:
- usage of nose replaced with testr
- now all the tests are thread safe
- added new options for run_tests.sh, such as --concurrency, --debug, etc...
- new '--concurrency' option for run_tests.sh defaults to 1, examples:
    ./run_tests.sh  # will run in 1 thread
    ./run_tests.sh --concurrency 2  # will run tests in 2 threads
- added tools/colorizer.py for colorizing output of testrun with run_tests.sh
- tests running with tox use as much threads as cores available by default
- examples of testrun with tox:
    tox  # will run test suites defined with 'envlist' in tox.ini, now it is pep8,py26,py27
    tox -epy27  # amount of threads is equal to amount of cores
    tox -epy27 -- --concurrency=2  # amount of threads is 2
    tox -epy27 -- --concurrency=4  # amount of threads is 4
- Added 'Database' class to manila.test module, for more conveniant db testing
- updated policy file 'manila/tests/policy.json' to allow share-network actions
- removed nose-related requirements
- added new requirements for testrepository, subunit

With merge of this change all old installed virtual environments become
incompatible and should be removed with "rm -rf .tox .venv" before testrun.

Implements blueprint testr-with-unittests

Change-Id: I9579ecd538e29d478dbc12adc7dcc33fc668b397