Prevent lldb-vscode tests from source lldbinit file

lldb-vscode is hard-coded to source .lldbinit file which causes some tests to
fail on my machine.
This patch adds a new option to control this:
1. vscode.py and lldb-vscode tests will not source .lldbinit by default
2. lldb-vscode will source .lldbinit in production if not specified otherwise

Differential Revision: https://reviews.llvm.org/D135620