Dockerfile: Add gnupg package

- gnupg is currently installed into kas-docker due to reprepro's
requirement. Hence, available only in isar version of kas-docker.
- Add gnupg explicitly in Dockerfile. It is needed for both isar and
yocto builds.

Signed-off-by: Vijai Kumar K <Vijaikumar_Kanagarajan@mentor.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Dockerfile

@@ -16,7 +16,7 @@ RUN apt-get install --no-install-recommends -y \
                        tar bzip2 curl dosfstools mtools parted \
                        syslinux tree python3-pip bc python3-yaml \
                        lsb-release python3-setuptools ssh-client \
-                       vim less mercurial iproute2 xz-utils && \
+                       vim less mercurial iproute2 xz-utils gnupg && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*