Update the IT Dockerfile to reduce the image size (NVIDIA#766)

- Assembled all the installations in one RUN
- Cleaned the conda cache files after all the installations done
- Removed the duplicate python3.6

Signed-off-by: Firestarman <firestarmanllc@gmail.com>

jenkins/Dockerfile.integration.centos7

@@ -26,9 +26,7 @@ FROM nvidia/cuda:${CUDA_VER}-runtime-centos7
 #Install java-8, maven, docker image
 RUN yum update -y && \
     yum install -y centos-release-scl && \
-    yum install -y java-1.8.0-openjdk-devel \
-    wget rh-python36
-
+    yum install -y java-1.8.0-openjdk-devel wget
 
 # The default mvn verision is 3.05 on centos7 docker container.
 # The plugin: net.alchim31.maven requires a higher mvn version.
@@ -38,27 +36,24 @@ RUN wget ${URM_URL}/org/apache/maven/apache-maven/3.6.3/apache-maven-3.6.3-bin.t
     tar xzvf $MAVEN_HOME-bin.tar.gz -C /usr/local && \
     rm -f $MAVEN_HOME-bin.tar.gz
 
-ENV PATH "$MAVEN_HOME/bin:/opt/rh/rh-python36/root/usr/bin/:$PATH"
+ENV PATH "$MAVEN_HOME/bin:$PATH"
 
 RUN wget --quiet https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh -O ~/miniconda.sh && \
     /bin/bash ~/miniconda.sh -b -p /opt/conda
 
-RUN . /opt/conda/bin/activate && \
-    conda init
-
 ENV PATH="/opt/conda/bin:${PATH}"
 
-RUN conda --version
+RUN . /opt/conda/bin/activate && \
+    conda init && \
+    conda --version
 
 ARG CUDA_TOOLKIT_VER=10.1
-RUN conda install -c rapidsai -c nvidia -c conda-forge \
-    -c defaults cudf=0.15 python=3.7 cudatoolkit=${CUDA_TOOLKIT_VER}
-
-RUN conda install spacy && \
-    python -m spacy download en_core_web_sm
-
-RUN conda install -c anaconda pytest requests pandas pyarrow
-RUN conda install -c conda-forge sre_yield
+RUN conda install -y -c rapidsai -c nvidia -c conda-forge -c defaults cudf=0.15 python=3.7 cudatoolkit=${CUDA_TOOLKIT_VER} && \
+    conda install -y spacy && \
+    python -m spacy download en_core_web_sm && \
+    conda install -y -c anaconda pytest requests pandas pyarrow && \
+    conda install -y -c conda-forge sre_yield && \
+    conda clean -ay
 
 # Set ENV for mvn
 ENV JAVA_HOME "/usr/lib/jvm/java-1.8.0-openjdk"