[ci] migrate to new Dockerfile (#2174)

* migrate Dockerfile

* switch tag back

.ci/README.md

+Helper Scripts for CI
+=====================
+
+This folder contains scripts which are run on CI services.
+
+Dockerfile used on CI service is maintained in a separate [GitHub repository](https://github.com/guolinke/lightgbm-ci-docker) and can be pulled from [Docker Hub](https://hub.docker.com/r/lightgbm/vsts-agent).

.ci/dockers/ubuntu-14.04/Dockerfile

-FROM microsoft/vsts-agent:ubuntu-14.04
-
-# Install basic command-line utilities
-RUN apt-get update \
- && apt-get install -y --no-install-recommends \
-    curl \
-    locales \
-    sudo \
-    unzip \
-    wget \
-    zip \
- && rm -rf /var/lib/apt/lists/*
-
-# Setup the locale
-ENV LANG en_US.UTF-8
-ENV LC_ALL $LANG
-RUN locale-gen $LANG \
- && update-locale
-
-# Install essential build tools
-RUN apt-get update \
- && apt-get install -y --no-install-recommends \
-    build-essential \
- && rm -rf /var/lib/apt/lists/*
-
-# Install clang 7.0
-RUN add-apt-repository ppa:ubuntu-toolchain-r/test -y \
- && cd /tmp \
- && wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add - \
- && add-apt-repository "deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-7 main" -y \
- && apt-get update \
- && apt-get install -y --no-install-recommends \
-    clang-7 \
-    libomp-7-dev \
- && rm -rf /var/lib/apt/lists/*
-
-# Install CMake
-RUN curl -sL https://cmake.org/files/v3.14/cmake-3.14.1-Linux-x86_64.sh -o cmake.sh \
- && chmod +x cmake.sh \
- && ./cmake.sh --prefix=/usr/local --exclude-subdir \
- && rm cmake.sh
-
-# Install Java
-RUN add-apt-repository ppa:openjdk-r/ppa -y \
- && apt-get update \
- && apt-get install -y --no-install-recommends \
-    openjdk-8-jdk \
- && rm -rf /var/lib/apt/lists/*
-
-ENV JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
-
-# Install SWIG
-RUN curl -sL https://downloads.sourceforge.net/project/swig/swig/swig-3.0.12/swig-3.0.12.tar.gz -o swig.tar.gz \
- && tar -xzf swig.tar.gz \
- && cd swig-3.0.12 \
- && ./configure --prefix=/usr/local --without-pcre \
- && make \
- && make install \
- && cd .. \
- && rm swig.tar.gz \
- && rm -rf swig-3.0.12
-
-# Install Miniconda
-RUN curl -sL https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -o miniconda.sh \
- && chmod +x miniconda.sh \
- && ./miniconda.sh -b -p /opt/conda \
- && rm miniconda.sh \
- && /opt/conda/bin/conda install python=3 -q -y \
- && /opt/conda/bin/conda install mkl qt -q -y \
- && /opt/conda/bin/conda clean -a -y \
- && chmod -R 777 /opt/conda
- 
-ENV CONDA=/opt/conda/
-
-# Clean system
-RUN apt-get clean \
- && rm -rf /var/lib/apt/lists/* \
- && rm -rf /etc/apt/sources.list.d/* \
- && rm -rf /tmp/*