Building for core18: multipass issue

[Lin-Buo-Ren]

@TimSueberkrueb

How do I directly build on the host system, nowadays?

Refer:

The SNAPCRAFT_BUILD_ENVIRONMENT environment variable

Synopsis Handle the chosen build provider. Description To determine the build environment, SNAPCRAFT_BUILD_ENVIRONMENT is retrieved from the environment and used to determine the build provider. An environment can be forced by use of force_provider during initialization. The default environment is multipass unless the snapcraft is run inside docker for which the preferred environment will be to use the host. Valid values are: host: the host will drive the build. managed-host: the host will d…