Fix pip install line in Dockerfile

[thopre]

Summary

The pip install line in Dockerfile is missing the -r switch and is
not executed from the directory where the requirement file is, both of
which make the docker image fail to build. This commit fixes those
issues and also simplify the line by using pip3 instead of
python3 -m pip.

Test Plan: cd docker && docker-compose build work successfully with this
patch.

[cmatthews]

Thanks, I didn’t have a system to check my changes on!

[thopre]

Landed as 4757dfc076886bd581b548f021026ea8163737cb

docker/Dockerfile

 FROM python:alpine
 
 RUN apk update \
   && apk add --no-cache --virtual .build-deps git g++ postgresql-dev yaml-dev \
   && apk add --no-cache libpq \
   && git clone https://github.com/llvm/llvm-lnt /var/src/lnt \
-  && python3 -m pip install /var/src/lnt/requirements.server.txt \
+  && cd /var/src/lnt && pip3 install -r requirements.server.txt \
   && rm -rf /var/src \
   && apk --purge del .build-deps \
   && mkdir /var/log/lnt
 
 COPY docker-entrypoint.sh wait_db /usr/local/bin/
 
 VOLUME /var/log
 
 EXPOSE 8000
 
 ENV DB_ENGINE= DB_HOST= DB_USER= DB_PWD= DB_BASE=
 
 ENTRYPOINT docker-entrypoint.sh