Add tests demonstrating V8 Port error handling

[dpezely]

V8 errors available through erlang_v8 offer insufficient granularity for graceful recovery of those errors.

Fixing that requires reaching beyond the C++ Erlang Port to resolve. However, V8 docs don't easily accommodate cherry-picking one's way through for our purposes here, and acquiring the necessary perspective on V8 internals goes beyond our current time constraints, unfortunately.

Instead for our purposes with router, we can handle those errors by stop/start of V8 VM.

This PR adds tests and code comments demonstrating existing erlang_v8 behavior.