Run tests parallel by default

Remove `--concurrency 1` option from tox.ini which would entail
a parallel test execution.
Add @mock decorator to test methods that have mock objects to make
cleanup correct.
Add store.configure() to configure store properly.

Change-Id: I4b58746f6b6ad037fabb29be5ca1d1febcb0cf95
Merge "Run tests parallel by default"