Update travis config for new test matrix

This commit updates the travis config to reflect the new release stream for
logstash. In addition to the new test cells we use the upstream docker-setup.sh
script from the upstream `.ci` repo.

Author: donoghuc

.ci/docker-setup.sh

@@ -4,13 +4,15 @@ import:
 before_install:
 - sudo sysctl -w vm.max_map_count=262144 # due ES bootstrap requirements
 
-env:
-- INTEGRATION=false ELASTIC_STACK_VERSION=7.x
-- INTEGRATION=false ELASTIC_STACK_VERSION=8.x
-- INTEGRATION=false ELASTIC_STACK_VERSION=7.x SNAPSHOT=true
-- INTEGRATION=false ELASTIC_STACK_VERSION=8.x SNAPSHOT=true
-- INTEGRATION=true ELASTIC_STACK_VERSION=7.x
-- INTEGRATION=true ELASTIC_STACK_VERSION=7.x SNAPSHOT=true LOG_LEVEL=info
-- INTEGRATION=true ELASTIC_STACK_VERSION=8.x SNAPSHOT=true LOG_LEVEL=info
-- SECURE_INTEGRATION=true INTEGRATION=true ELASTIC_STACK_VERSION=7.x LOG_LEVEL=info
-- SECURE_INTEGRATION=true INTEGRATION=true ELASTIC_STACK_VERSION=7.x ES_SSL_SUPPORTED_PROTOCOLS=TLSv1.3
+jobs:
+  include:
+    - stage: "Integration Tests"
+    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=7.current
+    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.previous
+    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.current
+    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.next
+    - env: INTEGRATION=true SNAPSHOT=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.future
+    - stage: "Secure Integration Tests"
+    - env: SECURE_INTEGRATION=true INTEGRATION=true LOG_LEVEL=info ELASTIC_STACK_VERSION=8.current SNAPSHOT=true
+    - env: SECURE_INTEGRATION=true INTEGRATION=true LOG_LEVEL=info ELASTIC_STACK_VERSION=7.current
+    - env: SECURE_INTEGRATION=true INTEGRATION=true LOG_LEVEL=info ELASTIC_STACK_VERSION=7.current ES_SSL_SUPPORTED_PROTOCOLS=TLSv1.3