Update Dockerfiles to 18.04
Fixes bug 1291
Change-Id: Ia4f529242ed3ef7a3d3f07cb67d5ee36447bc5d6
Signed-off-by: 
beierlm <mark.beierl@canonical.com>
Fixes bug 1291
Change-Id: Ia4f529242ed3ef7a3d3f07cb67d5ee36447bc5d6
Signed-off-by: beierlm <mark.beierl@canonical.com>