Snap promotion fix

Changes snapcraft to run directly on host instead of in docker
continer.  This adds the requirement to have snapcraft installed
in the Jenkins agent, but is more reliable as the snapcraft docker
image is not the best practice anymore for building snaps.

Change-Id: I3c26773a4989551da92a0015749717fe2d622b22
Signed-off-by: beierlm <mark.beierl@canonical.com>