Speedup build: introduced SharedSqlTestDatabase and DisposableSqlTestDatabase junit extensions

[a-sayyed]

Extracted shared database logic from PR https://github.com/eclipse/hawkbit/pull/1126 (goal state).

This is an intermediate state, where the tests

• reuse the generated databases - one generated db per jvm process (surefire.forkCount)
• use a single tenant for all the tests
• Have the CleanupTestExecutionListener run after each method

Only two tests require an own database: SystemManagementTest and MultiTenancyEntityTest since they modify the default tenant

[hawkbit-bot]

Can one of the admins verify this patch?