Sync install_venv_common.py from oslo-incubator

This is needed to ensure that when using run_tests.sh requirements
are handled correctly. Both requirements.txt and test-requirements.txt
need to be handed to pip at the same time to ensure that all
dependencies are satisfied and we don't upgrade a package to be
outside of the version constraints set by requirements.txt when
installing dependencies for the packages in test-requirements.txt.

Change-Id: I89bcf4e44b7274dca535e8e1d2eeb0adb142cabb
README.rst of tempest stress is misleading

Change-Id: I6f533766c4c19023eff2ffa3fc62f6e1f82a4215
Closes-Bug: #1229299
Move LockFixture to tempest.common

This commit moves LockFixture used for locking between tests out of
tempest.api.compute.admin.test_aggregates and into tempest.common.

Change-Id: I14431617c88c62b6da4383668ffa635a12c1b071
Merge "README.rst of tempest stress is misleading"
Merge "Sync install_venv_common.py from oslo-incubator"
Merge "Move LockFixture to tempest.common"