Dockerise Gatling tests

Dockerising the tests will help when running them from the CI.

Feature: Issue 11908
Change-Id: I15432b2246a2e6eda393fe885931488662d29f3e

e2e-tests/load-tests/Dockerfile

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+FROM denvazh/gatling:3.2.1
+
+ARG gatling_git_version=1.0.9
+RUN apk add --no-cache maven
+RUN mvn dependency:get \
+        -DgroupId=com.gerritforge \
+        -DartifactId=gatling-git_2.12 \
+        -Dversion=$gatling_git_version \
+        -Dtype=pom
+RUN mvn dependency:copy-dependencies \
+        -f /root/.m2/repository/com/gerritforge/gatling-git_2.12/$gatling_git_version/gatling-git_2.12-$gatling_git_version.pom \
+        -DoutputDirectory=/opt/gatling/lib/
+RUN mvn dependency:get \
+        -Dartifact=com.gerritforge:gatling-git_2.12:$gatling_git_version:jar \
+        -Ddest=/opt/gatling/lib/gatling-git.jar
+
+ARG gatling_home=/home/gatling
+RUN addgroup -g 1000 -S appgroup && \
+        adduser -u 1000 -S gatling -G appgroup -h $gatling_home
+RUN cp -R /opt/gatling/* $gatling_home && \
+        chown -R gatling:appgroup $gatling_home
+
+WORKDIR $gatling_home
+USER gatling
+
+COPY ./src/test/scala/com/google/gerrit/scenarios $gatling_home/user-files/simulations
+COPY ./src/test/resources/application.conf $gatling_home/conf
+COPY ./src/test/resources/data $gatling_home/user-files/resources/data
+
+ENV GATLING_HOME=$gatling_home
+
+ENTRYPOINT ["/home/gatling/bin/gatling.sh"]

e2e-tests/load-tests/README.md

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+# How to build the Docker image
+
+```$shell
+docker build . -t e2e-tests
+```
+
+# How to run a test
+
+```$shell
+docker run -it e2e-tests -s com.google.gerrit.scenarios.ReplayRecordsFromFeederScenario
+```