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
cluster: allow multiple calls to setupMaster()

Only attributes of 'cluster.settings' will be modified after the first
call, leaving all other cluster initialization alone. Each call that
includes a 'settings' argument triggers a 'setup' event to be emitted.

Instead of each call resetting all values to their defaults, use the
current settings (if any) as the default. This retains setupMaster's
support how cluster.fork() uses setupMaster() to ensure
cluster.settings has been populated.

Update example in docs to use current node coding style and include
an example of progressive configuration.
cluster: include settings object in 'setup' event

Emits on every call to cluster.setupMaster(), even if no new settings
are given. This is because calling cluster.setupMaster() without
arguments (or with an empty options object) results in the settings
being restored to their defaults.