Fixed tests from recent changed.  Detect test now calles exists.  Install now returns as string, not list.
Added ability to customize the arguments for `composer install`.
Defaults to `--no-interaction` and `--no-dev`.  The `--no-progress`
option is always set, as we don't want progress display which might
break the script.  Added test to confirm.
Added sanity check for presence of `composer.lock`.  If it doesn't
exist, a warning will be printed.