Clean up spawn error when sub-command not found

Currently when `component` attempts to spawn a sub-command not found in the users path it outputs:
```shell
execvp(): No such file or directory

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: spawn ENOENT
    at errnoException (child_process.js:975:11)
    at Process.ChildProcess._handle.onexit (child_process.js:766:34)
```
Changed this to display the default help message, provided by `program.help()`, when an absolute path to the executable cannot be found. Duplicate executables within a user's path are resolved to the last entry.