Test: Create a TestBase which allows inserting custom model to run queries

[smitpatel]

We need to make QueryBugsTest provider agnostic so we can get better coverage. This is important since most of the model we add here are customer models.

[smitpatel]

Adding few more points, which are related and should be considered.
QueryBugsTest creates database only once but populate it with tables and data for each test.
Context different test scenario

• Separate bounderies
• Creates only required tables and seed them
• Easy to see data and test together

Single context for all test

• We can go into normal flow of other test classes by having a model which just add more entityTypes in future
• Database is initialized only once and reused

[AndriySvyryd]

Tests the require MARS should be moved out and marked with SqlServerCondition.SupportsMARS. See 68c1a5f, 97bf494, #1015

Also create a TestStoreFixtureBase and use it where SharedStoreFixtureBase is used but the database does not actually needs to be shared (almost everything except Northwind). And move tests that invoke SaveChanges from QueryBugsTest to EndToEndTests