Linearizability Tests for Storage Engine

[ambud]

Summary:
Add linearizability tests for Storage Engine.

Description:
Sidewinder, just like any other database supports concurrent access, which involves concurrency support for both reads and writes. It's important for the database to guarantee the linearizability property to ensure there are no concurrency bugs.

Tests should cover the following:

• Two or more concurrent threads writing 1 series (sequence ordering)
• Two or more concurrent threads performing reads
• Two or more concurrent threads performing reads and writes simultaneously