integration tests: Refactoring for dynamic project configurations

  o CliIntegration.run() now takes a `project_config` option, this
    will be composited on top of the existing, substituted project.conf

  o Removing gnomesdk alias from integration tests project.conf

  o Using `sysroot` alias instead of `gnome7` alias

  o Make base-alpine.bst use the `sysroot` alias now

  o Removed `create_project_config()` from shell.py tests, now
    use the new built-in feature for this which is cleaner.