[Python Build] Add python-dev to pulsar standalone docker image (apac…

…he#7871)

Motivation
Follow apache#7857 In the pulsar standalone Dockerfile, we also need to do the same operation

Modifications
Add python2.7-dev to pulsar standalone docker image

docker/pulsar-standalone/Dockerfile

@@ -28,8 +28,8 @@ FROM openjdk:8-jdk
 
 # Note that the libpq-dev package is needed here in order to install
 # the required python psycopg2 package (for postgresql) later
-RUN apt-get update
-RUN apt-get -y install python2.7 python-pip postgresql sudo nginx supervisor libpq-dev
+RUN apt-get update \
+    && apt-get -y install python2.7 python2.7-dev python-pip postgresql sudo nginx supervisor libpq-dev
 
 # Postgres configuration
 COPY --from=dashboard /etc/postgresql/11/main/postgresql.conf /etc/postgresql/11/main/postgresql.conf