issue #275: Travis build matrix from hell.

dev_requirements.txt:
- drop debops, it's not available for Python2.6

.travis.yml

@@ -9,20 +9,53 @@ notifications:
 language: python
 cache: pip
 
-python:
-- "2.7"
-
-env:
-- MODE=mitogen DISTRO=debian
-- MODE=mitogen DISTRO=centos
-- MODE=debops_common VER=2.4.3.0
-- MODE=debops_common VER=2.5.1
-# Ansible tests.
-- MODE=ansible VER=2.4.3.0 DISTRO=debian
-- MODE=ansible VER=2.5.1 DISTRO=centos
-- MODE=ansible VER=2.5.1 DISTRO=debian
-# Sanity check our tests against vanilla Ansible, they should still pass.
-- MODE=ansible VER=2.5.1 DISTRO=debian STRATEGY=linear
+matrix:
+  include:
+    # Mitogen tests.
+    # 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=mitogen DISTRO=debian
+    # 2.7 -> 2.6
+    - python: "2.7"
+      env: MODE=mitogen DISTRO=centos6
+    # 2.6 -> 2.7
+    - python: "2.6"
+      env: MODE=mitogen DISTRO=centos7
+    # 2.6 -> 2.6
+    - python: "2.6"
+      env: MODE=mitogen DISTRO=centos6
+
+    # Debops tests.
+    # 2.4.3.0; 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=debops_common VER=2.4.3.0
+    # 2.5.5; 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=debops_common VER=2.5.5
+
+    # ansible_mitogen tests.
+    # 2.4.3.0; Debian; 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=ansible VER=2.4.3.0 DISTRO=debian
+    # 2.5.5; Debian; 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=ansible VER=2.5.5 DISTRO=debian
+    # 2.5.5; CentOS; 2.7 -> 2.7
+    - python: "2.7"
+      env: MODE=ansible VER=2.5.5 DISTRO=centos7
+    # 2.5.5; CentOS; 2.7 -> 2.6
+    - python: "2.7"
+      env: MODE=ansible VER=2.5.5 DISTRO=centos6
+    # 2.5.5; CentOS; 2.6 -> 2.7
+    - python: "2.6"
+      env: MODE=ansible VER=2.5.5 DISTRO=centos7
+    # 2.5.5; CentOS; 2.6 -> 2.6
+    - python: "2.6"
+      env: MODE=ansible VER=2.5.5 DISTRO=centos6
+
+    # Sanity check our tests against vanilla Ansible, they should pass.
+    - python: "2.7"
+      env: MODE=ansible VER=2.5.5 DISTRO=debian STRATEGY=linear
 
 install:
 - pip install -r dev_requirements.txt

dev_requirements.txt

@@ -3,7 +3,6 @@ ansible==2.5.2
 coverage==4.5.1
 Django==1.6.11; python_version < '2.7'
 Django==1.11.5; python_version >= '2.7' # for module_finder_test
-debops==0.7.2
 mock==2.0.0
 pytest-catchlog==1.2.2
 pytest==3.1.2