Jenkins Pipeline with matrix testing

Jenkinsfile

node {
    stage 'Checkout'
    git branch: 'production', url: 'https://github.com/cdenneen/control-repo.git'
    stash "${env.JOB_NAME}"
    stage: 'Test'
    gitCommit = sh(returnStdout: true, script: 'git rev-parse HEAD').trim()
    // short SHA, possibly better for chat notifications, etc.
    shortCommit = gitCommit.take(6)
    sh "echo $shortCommit"
    def matrix = [:]
    def rubyVersion = ['2.1.10', '2.3.3']
    for (int x = 0; x < rubyVersion.size(); x++) {
        def puppetVersion = ['4.7.1', '4.8.1', '4.9.4']
        for (int i = 0; i < puppetVersion.size(); i++) {
            RUBY_VERSION = rubyVersion[x]
            PUPPET_GEM_VERSION = puppetVersion[i]
//            matrix["version_r${rubyVersion[x]}_p${puppetVersion[i]}"] = {
                withRvm("ruby-${RUBY_VERSION}") {
                    withEnv(["PUPPET_GEM_VERSION=${PUPPET_GEM_VERSION}"]) {
                        stage("ruby-${RUBY_VERSION} and puppet-${PUPPET_GEM_VERSION}") {
                            echo "$RUBY_VERSION + $PUPPET_GEM_VERSION"
                        }
                        stage("spec r${RUBY_VERSION}p${PUPPET_GEM_VERSION}") {
                            sh 'gem install bundler --no-ri --no-rdoc'
                            sh 'bundle install'
                        }
                        stage('Do Puppet Code Validation') {
                            sh 'bundle exec rake validate'
                        }
                    }
                }
//            }
        }
    }
//    parallel matrix 
}
 def withRvm(version, cl) {
  withRvm(version, "executor-${env.EXECUTOR_NUMBER}") {
        cl()
    }
}

def withRvm(version, gemset, cl) {
    RVM_HOME='$HOME/.rvm'
    paths = [
        "$RVM_HOME/gems/$version@$gemset/bin",
        "$RVM_HOME/gems/$version@global/bin",
        "$RVM_HOME/rubies/$version/bin",
        "$RVM_HOME/bin",
        "${env.PATH}"
    ]

    def path = paths.join(':')

    // withEnv(["PATH=${env.PATH}:$RVM_HOME", "RVM_HOME=$RVM_HOME"]) {
    withEnv(["PATH=$path:$RVM_HOME", "RVM_HOME=$RVM_HOME"]) {
        sh "set +x; source $RVM_HOME/scripts/rvm; rvm use --create --install --binary $version@$gemset"
    }

    withEnv([
        "PATH=$path",
        "GEM_HOME=$RVM_HOME/gems/$version@$gemset",
        "GEM_PATH=$RVM_HOME/gems/$version@$gemset:$RVM_HOME/gems/$version@global",
        "MY_RUBY_HOME=$RVM_HOME/rubies/$version",
        "IRBRC=$RVM_HOME/rubies/$version/.irbrc",
        "RUBY_VERSION=$version"
        ]) {
        'gem install bundler'
            cl()
        }
}

output.txt

Started by user Jenkins
[Pipeline] node
Running on master in /var/jenkins_home/workspace/newtestrvm
[Pipeline] {
[Pipeline] stage (Checkout)
Using the ‘stage’ step without a block argument is deprecated
Entering stage Checkout
Proceeding
[Pipeline] git
 > git rev-parse --is-inside-work-tree # timeout=10
Fetching changes from the remote Git repository
 > git config remote.origin.url https://github.com/cdenneen/control-repo.git # timeout=10
Fetching upstream changes from https://github.com/cdenneen/control-repo.git
 > git --version # timeout=10
 > git fetch --tags --progress https://github.com/cdenneen/control-repo.git +refs/heads/*:refs/remotes/origin/*
 > git rev-parse refs/remotes/origin/production^{commit} # timeout=10
 > git rev-parse refs/remotes/origin/origin/production^{commit} # timeout=10
Checking out Revision 2d0a4090863c173818fa546732d29b05108845be (refs/remotes/origin/production)
 > git config core.sparsecheckout # timeout=10
 > git checkout -f 2d0a4090863c173818fa546732d29b05108845be
 > git branch -a -v --no-abbrev # timeout=10
 > git branch -D production # timeout=10
 > git checkout -b production 2d0a4090863c173818fa546732d29b05108845be
 > git rev-list 2d0a4090863c173818fa546732d29b05108845be # timeout=10
[Pipeline] stash
Stashed 59 file(s)
[Pipeline] sh
[newtestrvm] Running shell script
+ git rev-parse HEAD
[Pipeline] sh
[newtestrvm] Running shell script
+ echo 2d0a40
2d0a40
[Pipeline] withEnv
[Pipeline] {
[Pipeline] sh
[newtestrvm] Running shell script
+ set +x
Using /var/jenkins_home/.rvm/gems/ruby-2.1.10 with gemset executor-4
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] withEnv
[Pipeline] {
[Pipeline] withEnv
[Pipeline] {
[Pipeline] stage
[Pipeline] { (ruby-2.1.10 and puppet-4.7.1)
[Pipeline] echo
2.1.10 + 4.7.1
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (spec r2.1.10p4.7.1)
[Pipeline] sh
[newtestrvm] Running shell script
+ gem install bundler --no-ri --no-rdoc
/var/jenkins_home/workspace/newtestrvm@tmp/durable-c92c3934/script.sh: line 2: gem: command not found
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] }
[Pipeline] // withEnv
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
ERROR: script returned exit code 127
Finished: FAILURE

Rev 5 works... Rev 6 moving RUBY_VERSION and PUPPET_GEM_VERSION inside the matrix makes them return null

Rev7 while it evaluates it's not matching the matrix... see lines 35-41 for example