Minor fixes and enhancements in local-build.sh

- Typo in the --help: --install-local-regitstry --> --install-local-registry
- Fix conditional. When VIM_AUTH_URL does not exist, the script was
showing this error message: "bash: [: too many arguments"
- Change from xip.io to nip.io
- Parameterize the osm/tests image tag. This allows to use the published
osm/tests image without needing to execute the stage-3 command
- Add print_section function: Cleaner way of printing section
information
- Add --vim-vca option. Allows to attach an existing VCA (registered in
OSM) to be used by the VIM account.

Change-Id: I2c1375e031f042f505f126586c0e819c21e1dd4c
Signed-off-by: David Garcia <david.garcia@canonical.com>