migration test support

[nurali-techie]

PR#21 added migration functionality to f8-common.

There are also some common functionality which used to test migration. This issue should bring those common migration test support to f8-common.

1. migrateToVersion link
2. executeSQLTestFile link

For context, check - comment

Note: migration functionality is changed a bit in f8-common (for ex, Migrations has no more external visibility). So we should check if above stuff can be achieved in better way.

One minor change:
change testmigration_test.go to migration_example_test.go and add doc.go for using migration_example_test.go.