Add procps to packages in Dockerfile

There are some DIB methods which need to use it which means
that DIB image builds will fail without it (and procps is
not included in the base Docker image)

Change-Id: I3cf3ce765a91a93e72465739ce68bc1238955126

Dockerfile

@@ -72,6 +72,7 @@ RUN \
       ubuntu-keyring \
       vhd-util \
       debootstrap \
+      procps \
       yum \
       yum-utils \
   && apt-get clean \