Optimize Dockerfile/image size

[misterbisson]

I believe the following portion of the Dockerfile can be combined into a single RUN statement that removes gcc and python-dev after doing the pip install, similarly to https://github.com/autopilotpattern/nfsserver/blob/wip/Dockerfile#L8-L19 .

RUN apt-get update \
    && apt-get install -y \
        python \
        python-dev \
        gcc \
        curl \
        percona-xtrabackup \
    && rm -rf /var/lib/apt/lists/*

# get Python drivers MySQL, Consul, and Manta
RUN curl -Ls -o get-pip.py https://bootstrap.pypa.io/get-pip.py && \
    python get-pip.py && \
    pip install \
        PyMySQL==0.6.7 \
        python-Consul==0.4.7 \
        manta==2.5.0

[tgross]

Released in https://github.com/autopilotpattern/mysql/releases/tag/5.6r2.2.0