child_process: copy spawnSync() cwd option to proper buffer

The spawnSync() cwd option was being copied to the incorrect
location. This commit copies to the correct location.

Closes #7824

Signed-off-by: Fedor Indutny <fedor@indutny.com>
src: pass the v8::Context to CreateEnvironment

Pass in the v8::Context, instead of creating it
within CreateEnvironment.  This allows callers
to use a pre-existing context.

Signed-off-by: Fedor Indutny <fedor@indutny.com>
test: fix regress-GH-1726