Timeout parameter added to gvm::package

Default timeout is 300 seconds defined by Puppet. This causes the error in slower connections:

```
err: /Stage[main]//Gvm::Package[grails]/Exec[gvm install grails 2.3.7]/returns: change from notrun to 0 failed: Command exceeded timeout at /tmp/vagrant-puppet-1/modules-0/gvm/manifests/package.pp:46
```

Default value of new `timeout` parameter is 0 (means infinity).