updating build/test CI on master

.gitlab-ci.yml

 stages:
   - build
   - test
+  - integration
 
 # -- build ------------------
 .build: &build
@@ -63,14 +64,13 @@ build:el7:
     - popd
     - rm -rf dist/ligo-gracedb*
 
-build:debian:jessie:
-  <<: *build_debian
-  image: debian:jessie
-
 build:debian:stretch:
   <<: *build_debian
   image: debian:stretch
 
+build:debian:buster:
+  <<: *build_debian
+  image: debian:buster
 
 # -- test -------------------
 .test: &test
@@ -95,6 +95,45 @@ test:python3.7:
   <<: *test
   image: python:3.7
 
+# -- test -------------------
+.integration: &integration_test
+  stage: integration
+  image: python
+  variables:
+    TEST_SERVICE: https://gracedb-test.ligo.org/api/
+  before_script:
+    # source: https://wiki.ligo.org/AuthProject/LIGOCILOGONRobotCertificate
+    - echo 'debconf debconf/frontend select Noninteractive' | debconf-set-selections
+    - apt-get update && apt-get install -y curl krb5-user xsltproc
+    - echo "${ROBOT_KEYTAB}" | base64 -d | install -m 0600 /dev/stdin keytab
+    - ROBOT_PRINCIPAL=$(klist -k keytab | head -n 4 | tail -n 1 | sed -E 's/^.* +//')
+    - kinit $ROBOT_PRINCIPAL -k -t keytab
+    - ./scripts/ligo-proxy-init -k
+  script:
+    - python setup.py test --addopts "-m integration"
+  # Do not run jobs simultaneously to avoid concurrent superevent 
+  # creation. Staggering with when/start_in worked marginally. This
+  # was inspired by:
+  # https://about.gitlab.com/blog/2020/01/21/introducing-resource-groups/
+  # and gracedb_sdk's pipeline.
+  resource_group: integration-test
+
+integration:python2.7:
+  <<: *integration_test
+  image: python:2.7
+
+integration:python3.5:
+  <<: *integration_test
+  image: python:3.5
+
+integration:python3.6:
+  <<: *integration_test
+  image: python:3.6
+
+integration:python3.7:
+  <<: *integration_test
+  image: python:3.7
+
 # -- docs -------------------
 # Although we don't host the docs on Gitlab Pages,
 # we still want to check that they build properly.