ci(kitchen+travis): modify matrix to include develop platform

* Use balanced matrix based on `template-formula` guidelines
* Initial ref: https://github.com/saltstack-formulas/template-formula/issues/118

.travis.yml

@@ -11,29 +11,33 @@ language: ruby
 services:
   - docker
 
-before_install:
-  - bundle install
-
 # Make sure the instances listed below match up with
 # the `platforms` defined in `kitchen.yml`
 env:
   matrix:
-    - INSTANCE: default-debian-9-2019-2-py3
+    - INSTANCE: default-debian-9-develop-py3
+    # TODO: Re-enable this once the `systemd` service can be restarted reliably
+    # - INSTANCE: default-ubuntu-1804-develop-py3
+    # - INSTANCE: default-centos-7-develop-py3
+    # - INSTANCE: default-fedora-29-develop-py3
+    # - INSTANCE: default-opensuse-leap-15-develop-py3
+    # - INSTANCE: default-debian-9-2019-2-py3
     # TODO: Re-enable this once the `systemd` service can be restarted reliably
     # - INSTANCE: default-ubuntu-1804-2019-2-py3
     - INSTANCE: default-centos-7-2019-2-py3
-    # - INSTANCE: default-fedora-29-2019-2-py3
-    - INSTANCE: default-opensuse-leap-15-2019-2-py3
+    - INSTANCE: default-fedora-29-2019-2-py3
+    # - INSTANCE: default-opensuse-leap-15-2019-2-py3
     # - INSTANCE: default-debian-9-2018-3-py2
     - INSTANCE: default-ubuntu-1604-2018-3-py2
     # - INSTANCE: default-centos-7-2018-3-py2
-    - INSTANCE: default-fedora-29-2018-3-py2
-    # TODO: Use this when fixed instead of `opensuse-423`
-    # NOTE: Having to temporarily disable `opensuse-423` due to slow mirror
+    # - INSTANCE: default-fedora-29-2018-3-py2
+    # TODO: Use this when fixed instead of `opensuse-leap-42`
+    # Ref: https://github.com/netmanagers/salt-image-builder/issues/2
     # - INSTANCE: default-opensuse-leap-15-2018-3-py2
-    # - INSTANCE: default-opensuse-423-2018-3-py2
+    - INSTANCE: default-opensuse-leap-42-2018-3-py2
     # - INSTANCE: default-debian-8-2017-7-py2
     # - INSTANCE: default-ubuntu-1604-2017-7-py2
+    # TODO: Enable after improving the formula to work with other than `systemd`
     - INSTANCE: default-centos-6-2017-7-py2
     # - INSTANCE: default-fedora-28-2017-7-py2
     # - INSTANCE: default-opensuse-leap-42-2017-7-py2
@@ -73,4 +77,3 @@ jobs:
         script:
           # Run `semantic-release`
           - npx semantic-release@15
-