Use canvas-docker pool of agents

Closes CORE-3304

Test plan:
  Jenkins passes
  Verify builds run on canvas_docker nodes

Change-Id: I789531b8962d7ca53ff938951366a173ed69f2ca
Reviewed-on: https://gerrit.instructure.com/208506
Tested-by: Jenkins
Reviewed-by: James Butters <jbutters@instructure.com>
QA-Review: Robert Lamb <rlamb@instructure.com>
Product-Review: Robert Lamb <rlamb@instructure.com>

Jenkinsfile

@@ -46,7 +46,7 @@ def build_parameters = [
 ]
 
 pipeline {
-  agent { label 'docker' }
+  agent { label 'canvas-docker' }
 
   options {
     ansiColor('xterm')

Jenkinsfile.contract-tests

@@ -33,7 +33,7 @@ pipeline {
   // Todo: This will run all contract tests consecutively, still need to get parallel depending on runtime
   stages {
     stage ('Contract Tests') {
-      agent { label 'docker' }
+      agent { label 'canvas-docker' }
       steps {
         timeout(time: 60) {
           sh 'printenv | sort'

Jenkinsfile.frontend

@@ -31,7 +31,7 @@ def cleanupDocker () {
 
 
 pipeline {
-  agent { label 'docker' }
+  agent { label 'canvas-docker' }
   options {
     ansiColor('xterm')
   }

Jenkinsfile.rspec

@@ -33,7 +33,7 @@ pipeline {
   // Todo: This will run all rspec tests consecutively, still need to get parallel depending on runtime
   stages {
     stage ('Rspec Tests') {
-      agent { label 'docker' }
+      agent { label 'canvas-docker' }
       steps {
         timeout(time: 60) {
           sh 'printenv | sort'

Jenkinsfile.selenium.chrome

@@ -35,7 +35,7 @@ pipeline {
     stage ('Run Tests Parallel') {
       parallel {
         stage('Selenium Tests') {
-          agent { label 'docker' }
+          agent { label 'canvas-docker' }
           steps {
             timeout(time: 60) {
               sh 'printenv | sort'

Jenkinsfile.selenium.performance.chrome

@@ -33,7 +33,7 @@ pipeline {
   // Todo: This will run all performance tests consecutively, still need to get parallel depending on runtime
   stages {
     stage ('Selenium Performance Tests') {
-      agent { label 'docker' }
+      agent { label 'canvas-docker' }
       steps {
         timeout(time: 60) {
           sh 'printenv | sort'

Jenkinsfile.vendored-gems

@@ -19,7 +19,7 @@
  */
 
 pipeline {
-  agent { label 'docker' }
+  agent { label 'canvas-docker' }
   options {
     ansiColor('xterm')
   }

Jenkinsfile.xbrowser

@@ -33,7 +33,7 @@ pipeline {
   // Todo: This will run all xbrowser tests consecutively, still need to get parallel depending on runtime
   stages {
     stage ('Xbrowser Tests') {
-      agent { label 'docker' }
+      agent { label 'canvas-docker' }
       steps {
         timeout(time: 60) {
           sh 'printenv | sort'