title: pip install does not work from dockerfile
body: <p>I am getting following error while trying to run pip.</p>
  
  <pre><code>Could not open requirements file: [Errno 2] No such file or directory: '/home/elasticsearch/text-embeddings/requirements.txt'
  
  The command '/bin/sh -c pip3.6 install -r /home/elasticsearch/text-embeddings/requirements.txt' returned a non-zero code: 1
  </code></pre>
  
  <p>My dockerfile looks like this...</p>
  
  <pre><code>FROM elasticsearch:7.3.1
  
  RUN yum install -y https://centos7.iuscommunity.org/ius-release.rpm
  
  RUN yum update
  
  RUN yum install -y python36u python36u-libs python36u-devel python36u-pip git
  
  RUN mkdir /home/elasticsearch/
  RUN cd /home/elasticsearch/
  
  RUN git clone https://github.com/jtibshirani/text-embeddings.git
  
  WORKDIR /home/elasticsearch/text-embeddings
  
  RUN cd /home/elasticsearch/text-embeddings
  
  RUN pip3.6 install -r /home/elasticsearch/text-embeddings/requirements.txt
  
  CMD ["python3.6", "/home/elasticsearch/text-embeddings/src/main.py"]
  </code></pre>
  
  <p>I have checked that these commands run successfully on the server if run one command at a time from command-prompt.</p>