Clean up example execution

Motivation:

- example/pom.xml has quite a bit of duplication.
- We expect that we depend on npn-boot in more than one module in the
  near future. (e.g. handler, codec-http, and codec-http2)

Modification:

- Deduplicate the profiles in example/pom.xml
- Move the build configuration related with npn-boot to the parent pom.
- Add run-example.sh that helps a user launch an example easily

Result:

- Cleaner build files
- Easier to add a new example
- Easier to launch an example
- Easier to run the tests that relies on npn-boot in the future