update dockerfiles with pybind11

ci/docker_images/ubuntu/bionic/Dockerfile

@@ -48,10 +48,10 @@ RUN apt-get install -y libcairomm-1.0-dev
 RUN apt-get install -y python
 RUN apt-get install -y python-dev
 RUN apt-get install -y python-pip
+RUN apt-get install -y python-tk
 RUN apt-get install -y opencl-headers
 RUN apt-get install -y ocl-icd-libopencl1
 RUN apt-get install -y clinfo
-RUN apt-get install -y python-tk
 
 # python packages
 RUN pip install --upgrade pip
@@ -127,6 +127,7 @@ RUN ldconfig
 
 # pyopencl
 RUN cd /tmp                                       \
+&& pip install pybind11                           \
 && git clone https://github.com/inducer/pyopencl  \
 && cd pyopencl                                    \
 && git submodule update --init                    \

ci/docker_images/ubuntu/bionic_cuda/Dockerfile

@@ -127,6 +127,7 @@ RUN ldconfig
 
 # pyopencl
 RUN cd /tmp                                       \
+&& pip install pybind11                           \
 && git clone https://github.com/inducer/pyopencl  \
 && cd pyopencl                                    \
 && git submodule update --init                    \