Add variables with project and part-related content to the step execution environment. The variables are a subset of the variables set by Snapcraft and are prefixed by the name of the application using craft-parts. Additional application-specific environment variables can be defined by the application in the pre-step callback. The application_name string must be non-empty and contain only letters, digits or underscore characters. All other characters will be converted to underscores. If the application name starts with a digit, an underscore will be prepended to the step environment variable names. Signed-off-by: Claudio Matsuoka <claudio.matsuoka@canonical.com> - [x] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? -----