gistfile1.txt

PATH=~/bin:$PATH

sudo apt-get install git ant openjdk-7-jdk zip maven
sudo update-alternatives --config java

git clone https://gerrit.googlesource.com/buck ~/buck
cd ~/buck
ant
mkdir ~/bin
ln -s ~/buck/bin/buck ~/bin/

git clone https://gerrit.googlesource.com/gerrit ~/gerrit
cd ~/gerrit
git checkout stable-2.8
tools/download_all.py # might not be needed
buck build api
# patch tools/maven/fake_pom.xml based on https://gerrit-review.googlesource.com/#/c/44451/2
buck build api_install

# not sure which github-api to use...
git clone https://github.com/kohsuke/github-api.git ~/github-api
cd ~/github-api
git checkout github-api-1.45
mvn install -DskipTests

git clone https://github.com/lucamilanesio/github-api.git ~/github-api
cd ~/github-api
mvn install -DskipTests

wget https://gerrit-api.commondatastorage.googleapis.com/release/com/google/gerrit/gerrit-plugin-api/2.8/gerrit-plugin-api-2.8.jar
mvn install:install-file \
    -DgroupId=com.google.gerrit \
    -DartifactId=gerrit-plugin-api \
    -Dversion=2.8 \
    -Dpackaging=jar \
    -Dfile=gerrit-plugin-api-2.8.jar

git clone https://gerrit.googlesource.com/plugins/singleusergroup ~/singleusergroup
cd ~/singleusergroup
git checkout 3b8b28c47bec41554b6230fb257d9d43ee315086
mvn install

git clone https://gerrit.googlesource.com/plugins/github ~/github
cd ~/github
git checkout stable-2.8
mvn install # fails

As pointed out in [1] you shouldn't need to install Buck and compile Gerrit and deploy plugin-api in local Maven repository at all.

wget https://gerrit-api.commondatastorage.googleapis.com/release/com/google/gerrit/gerrit-plugin-api/2.8/gerrit-plugin-api-2.8.jar
mvn install:install-file \
    -DgroupId=com.google.gerrit \
    -DartifactId=gerrit-plugin-api \
    -Dversion=2.8 \
    -Dpackaging=jar \
    -Dfile=gerrit-plugin-api-2.8.jar

You still not able to fetch it without doing this manually? That's weird.
But if you are doing it anyway, why to compile Gerrit and install Buck at all?

[1] https://gerrit-review.googlesource.com/#/c/54083