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: I78a9d12d1c6e054f0fe886ccfe08472309100d0f
Signed-off-by: beierlm <mark.beierl@canonical.com>