When the test are run npm read the ~/.npmrc and ./.npmrc files and set some environment variables starting with `npm_`.
When the test create temporary folders and created a `.npmrc` the values there are ignored as the environment variables take precedence.
This commit remove this environment variable (from the local `process.env`) before starting the integrations test and restore them after. This way the `./.npmrc` files created in temp directory for the test are correctly used.

- Simplify the loop that check availability
- Increase timeout
- Remove the container after stopping

…Notes` plugins

Adapt tests and default value to the plugin definitions (`definitions.js`)

`npm` is called through `semantic-release` and in the integration test to make some assertion.
By isolating the the environment variables passed to `semantic-release` it's easier to avoid a mistake that would pass the test environment that contains is own auth variables.