add Dockerfile to integrate with OpenROAD unified build

.dockerignore

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+Dockerfile
+.dockerignore
+.gitignore
+
+# from .gitignore file
+*.o
+
+build
+build/*.*
+Makefile

Dockerfile

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+FROM centos:centos6 AS builder
+
+# install gcc 8
+RUN yum -y install centos-release-scl && \
+    yum -y install devtoolset-8 devtoolset-8-libatomic-devel
+ENV CC=/opt/rh/devtoolset-8/root/usr/bin/gcc \
+    CPP=/opt/rh/devtoolset-8/root/usr/bin/cpp \
+    CXX=/opt/rh/devtoolset-8/root/usr/bin/g++ \
+    PATH=/opt/rh/devtoolset-8/root/usr/bin:$PATH \
+    LD_LIBRARY_PATH=/opt/rh/devtoolset-8/root/usr/lib64:/opt/rh/devtoolset-8/root/usr/lib:/opt/rh/devtoolset-8/root/usr/lib64/dyninst:/opt/rh/devtoolset-8/root/usr/lib/dyninst:/opt/rh/devtoolset-8/root/usr/lib64:/opt/rh/devtoolset-8/root/usr/lib:$LD_LIBRARY_PATH
+
+RUN yum install -y wget git pcre-devel tcl-devel tk-devel bison flex \
+                   python-devel libxml2-devel libxslt-devel zlib-static glibc-static
+
+RUN wget http://prdownloads.sourceforge.net/swig/swig-4.0.0.tar.gz && \
+    tar -xf swig-4.0.0.tar.gz && \
+    cd swig-4.0.0 && \
+    ./configure && \
+    make && \
+    make install
+
+# installing cmake for build dependency
+RUN wget https://cmake.org/files/v3.14/cmake-3.14.0-Linux-x86_64.sh && \
+    chmod +x cmake-3.14.0-Linux-x86_64.sh  && \
+    ./cmake-3.14.0-Linux-x86_64.sh --skip-license --prefix=/usr/local
+
+# installing boost for build dependency
+RUN wget https://dl.bintray.com/boostorg/release/1.68.0/source/boost_1_68_0.tar.bz2 && \
+    tar -xf boost_1_68_0.tar.bz2 && \
+    cd boost_1_68_0 && \
+    ./bootstrap.sh && \
+    ./b2 install
+
+COPY . /TritonRoute
+RUN mkdir TritonRoute/build
+WORKDIR /TritonRoute/build
+RUN cmake ..
+RUN make
+
+
+FROM centos:centos6 AS runner
+RUN yum update -y && yum install -y tcl-devel
+COPY --from=builder /TritonRoute/build/TritonRoute /build/TritonRoute
+
+RUN useradd -ms /bin/bash openroad
+USER openroad
+WORKDIR /home/openroad