[BUGFIX] Use the vagrant user in development

php-fpm and nginx can have different permissions issues depending on the
vagrant host. This is because vagrant-rsync simply copies the file
permissions from the host.

To avoid this problem in the development vagrant, this changes the
application owner to the `vagrant` instead of `builddocstypo3org`. I
would guess that most developers have user read/write permissions even
if group permissions are read-only, so copying the permissions from the
host shouldn't be a problem anymore.

Another possible solution would be to add `--chmod 775` to the rsync
command, but switching to the vagrant user made the whole development
process just a bit simpler.