debuginfo: Add python formatters that allow LLDB to print values with Rust syntax
debuginfo: Inject 'Rust-mode' LLDB prelude into debuginfo test scripts.
debuginfo: Remove atexit()-debugger shutdown from lldb_batchmode.py

The shutdown call would always result in an exception being printed to standard error.
debuginfo: Add LLDB autotests to debuginfo test suite.

This commit adds LLDB autotests to the test suite but does not activate them by default yet.
debuginfo: Make sure that only one LLDB test task is run at a time.

Some older versions of LLDB have problems with multiple instances running in parallel. This commit makes sure we don't do that.
debuginfo: Enable LLDB autotests on apple-darwin.
debuginfo: Add a temporary hack for testing LLDB on the buildbots
debuginfo: Make some paths in compiletest absolute so the build bot doesn't trip over them.
debuginfo: Try to get minimal version of LLDB autotest framework running without crash with old LLDB version: Just create debugger instance in Python and do nothing else