[lldb-vscode] Fix two issues with runInTerminal test.

With ptrace_scope = 1 the kernel only allows tracing descendants of a
process. When using runInTerminal, the target process is not launched
by the debugger, so we need to modify LaunchRunInTerminal to explicitly
allow tracing. This should fix a problem reported in
https://reviews.llvm.org/D84974#3903716

In order to allow only the main lldb-vscode process to attach to the
target, this change introduces a new `--debugger-pid` flag that needs
to be passed with `--launch-target` and `--comm-file`.

Also, remove a special case from the launch method in the
lldbvscode_testcase test harness. The existing test was using
stopOnEntry, so the first stop didn't happen at the expected breakpoint
unless the harness did configurationDone first.

Differential Revision: https://reviews.llvm.org/D147805