Set healtcheck value to aws default one

[florian0410]

what

• Updating default healthcheck to AWS default one according to doc https://docs.aws.amazon.com/fr_fr/elasticbeanstalk/latest/dg/command-options-general.html#command-options-general-environmentprocess

why

• When deploying an empty environment (no application package deployed), AWS deploy a basic app. Its default process healthcheck is pointing to "/" in that case and not "/healthcheck".
• During many test, I got the situation where I wanted to update my environment without application just for testing. In the end, i forgot to setup this healthcheck value and lost a lot of time since I had to wait for beanstalk timeout. It does not occurs on first deployment it seems.

Note

I'm not sure if we also deploy an application package for the tests, in that module, I should add the default value to var file else.

[florian0410]

/test all

[nitrocode]

I forgot that this module is in a code freeze due to the sg module refactoring so after I merged this, I set the new release as a pre-release.

cloudposse/terraform-aws-security-group#17