Dockerfile: use tpm2software/tpm2-tss as base image

Using the organisation-wide Dockerfile as a base helps avoiding
duplicate efforts in keeping the image up to date.

Signed-off-by: Jonas Witschel <diabonas@gmx.de>

diff --git a/Dockerfile b/Dockerfile
index 9f32176..19301fb 100644
--- a/Dockerfile
+++ b/Dockerfile

@@ -1,48 +1,4 @@
-FROM ubuntu:18.04 AS base
-RUN apt-get update && apt-get install -y \
-    autoconf \
-    autoconf-archive \
-    automake \
-    build-essential \
-    doxygen \
-    gcc \
-    git \
-    libssl-dev \
-    libtool \
-    pkg-config \
-    wget
-
-# OpenSSL
-ARG openssl_name=openssl-1.1.0h
-WORKDIR /tmp
-RUN wget --quiet --show-progress --progress=dot:giga https://www.openssl.org/source/$openssl_name.tar.gz \
-	&& tar xvf $openssl_name.tar.gz \
-	&& rm /tmp/$openssl_name.tar.gz
-WORKDIR $openssl_name
-RUN ./config --prefix=/usr/local/openssl --openssldir=/usr/local/openssl \
-	&& make -j$(nproc) \
-	&& make install \
-	&& openssl version
-
-# IBM's Software TPM 2.0
-ARG ibmtpm_name=ibmtpm1119
-WORKDIR /tmp
-RUN wget --quiet --show-progress --progress=dot:giga "https://downloads.sourceforge.net/project/ibmswtpm2/$ibmtpm_name.tar.gz" \
-	&& sha256sum $ibmtpm_name.tar.gz | grep ^b9eef79904e276aeaed2a6b9e4021442ef4d7dfae4adde2473bef1a6a4cd10fb \
-	&& mkdir -p $ibmtpm_name \
-	&& tar xvf $ibmtpm_name.tar.gz -C $ibmtpm_name \
-	&& rm $ibmtpm_name.tar.gz
-WORKDIR $ibmtpm_name/src
-RUN CFLAGS="-I/usr/local/openssl/include" make -j$(nproc) \
-	&& cp tpm_server /usr/local/bin
-
-RUN apt-get install -y \
-    iproute2 \
-    libcmocka0 \
-    libcmocka-dev \
-    uthash-dev \
-    python3 \
-    clang
+FROM tpm2software/tpm2-tss AS base
 
 COPY . /tmp/tpm2-tss/
 WORKDIR /tmp/tpm2-tss