Class not found fix #643

[sergeypospelov]

Description

There were two problems:

• <clinit> executing happens in any thread, so UtContext could be empty and resolving classes inside static initializer failed, since we hadn't got the correct classloader. This is exactly what was going on and we were getting ClassNotFoundException in concrete execution.
• AccessControlException was wrapped in ExceptionInInitializerError, but we didn't handle it, so there were no comments about sandboxing.

Fixed these ones.

Fixes #643

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Manual Scenario

To Reproduce section from #643 and internal SAT issue passes.

Checklist:

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• No new warnings
• All tests pass locally with my changes