Pin grpc versions

Due to new version of grpc being released, the docker build
fails with errors.

Fixes bug 1200

Change-Id: Ifd958708a92a10a13c357fcd4f1960e6889ef89e
Signed-off-by: beierlm <mark.beierl@canonical.com>
(cherry picked from commit 2a815a3f98afa5fb180b2a47ee58c4f6dc7c69fb)
1 file changed