Add per-repo gerrit and zuul configuration

Remove ``.travis.yml`` after upstreaming to OpenStack.

Add missing ``py35`` target in tox.ini.

Note that upstream gate will be running py36 unit test but we do
want to keep the ``py35`` target for a broader set of test run in
the Canonical CI.

Hold gate test for Ubuntu Disco pending resolution of LP: #1824112

Change-Id: I17925206dbe4d3b3d51615552ca2afea42a049a6

.gitreview

@@ -0,0 +1,4 @@
+[gerrit]
+host=review.opendev.org
+port=29418
+project=openstack/charm-octavia-diskimage-retrofit.git

.travis.yml

@@ -1,6 +0,0 @@
-language: python
-python:
-  - "3.6"
-install: pip install tox-travis
-script:
-  - tox -e pep8,py3

.zuul.yaml

@@ -0,0 +1,4 @@
+- project:
+    templates:
+      - python36-charm-jobs
+      - openstack-cover-jobs

src/tests/tests.yaml

@@ -4,8 +4,11 @@ smoke_bundles:
 gate_bundles:
 - bionic-rocky
 - bionic-stein
-- disco
+comment: |
+  Deployment on Disco and onwards will not work until we resolve
+  https://bugs.launchpad.net/bugs/1824112
 dev_bundles:
+- disco
 - eoan
 target_deploy_status:
   glance-simplestreams-sync:

tox.ini

@@ -23,6 +23,11 @@ basepython = python3
 commands =
     charm-build --log-level DEBUG -o {toxinidir}/build src {posargs}
 
+[testenv:py35]
+basepython = python3.5
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
 [testenv:py36]
 basepython = python3.6
 deps = -r{toxinidir}/test-requirements.txt