Added composer commands to PHP Dockerfiles

tools/dockerfile/grpc_php/Dockerfile

@@ -46,4 +46,6 @@ RUN cd /var/local/git/grpc/src/php/ext/grpc \
   && ./configure \
   && make
 
+RUN cd /var/local/git/grpc/src/php && composer install
+
 RUN cd /var/local/git/grpc/src/php && ./bin/run_tests.sh

tools/dockerfile/grpc_php_base/Dockerfile

@@ -64,9 +64,12 @@ RUN apt-get update && apt-get install -y \
     sqlite3 \
     zlib1g-dev
 
-# Install the version of PHP gRPC is tested against
 ENV DEBIAN_FRONTEND noniteractive
 
+# Install composer
+RUN curl -sS https://getcomposer.org/installer | php
+RUN mv composer.phar /usr/local/bin/composer
+
 # Download the patched PHP protobuf so that PHP gRPC clients can be generated
 # from proto3 schemas.
 RUN git clone https://github.com/murgatroid99/Protobuf-PHP.git /var/local/git/protobuf-php