Replace travis build matrix with stages

With this change, the build first runs a single smoke screen build against the latest versions to save on build resources. Remaining topologies, server versions and PHP versions will be tested in parallel if this first build step was successful.

.travis.yml

@@ -19,51 +19,79 @@ env:
     - SERVER_VERSION=4.0.10
     - DEPLOYMENT=STANDALONE
 
-matrix:
-  fast_finish: true
+jobs:
+  allow_failures:
+    - php: "7.4snapshot"
+
   include:
-    - php: 5.6
-    - php: 7.0
-    - php: 7.1
-    - php: 7.2
-    - php: 7.3
-    - php: 7.0
+
+    - stage: Smoke Testing
+      php: "7.3"
+
+    # Test remaining supported PHP versions
+    - stage: Test
+      php: "5.6"
+    - stage: Test
+      php: "7.0"
+    - stage: Test
+      php: "7.1"
+    - stage: Test
+      php: "7.2"
+    - stage: Test
+      php: "7.4snapshot"
+
+      # Test older standalone server versions (3.0-3.6)
+    - stage: Test
+      php: "7.0"
       dist: trusty
       env:
         - SERVER_DISTRO=ubuntu1404
         - SERVER_VERSION=3.0.15
         - DEPLOYMENT=STANDALONE_OLD
-    - php: 7.0
+    - stage: Test
+      php: "7.0"
       env:
         - SERVER_VERSION=3.2.22
         - DEPLOYMENT=STANDALONE_OLD
-    - php: 7.0
+    - stage: Test
+      php: "7.0"
       env:
         - SERVER_VERSION=3.4.21
         - DEPLOYMENT=STANDALONE_OLD
-    - php: 7.0
+    - stage: Test
+      php: "7.0"
       env:
         - SERVER_VERSION=3.6.13
-    - php: 7.3
+
+    # Test other server configurations
+    - stage: Test
+      php: "7.3"
       env:
         - DEPLOYMENT=STANDALONE_AUTH
-    - php: 7.3
+    - stage: Test
+      php: "7.3"
       env:
         - DEPLOYMENT=STANDALONE_SSL
-    - php: 7.3
+    - stage: Test
+      php: "7.3"
       env:
         - SERVER_VERSION=3.6.13
         - DEPLOYMENT=REPLICASET
-    - php: 7.3
+    - stage: Test
+      php: "7.3"
       env:
         - DEPLOYMENT=REPLICASET
-    - php: 7.3
+    - stage: Test
+      php: "7.3"
+      env:
+        - DEPLOYMENT=SHARDED_CLUSTER
+
+    # Test upcoming server versions
+    - stage: Test
+      php: "7.3"
       env:
         - SERVER_VERSION=4.2.0-rc1
         - DEPLOYMENT=REPLICASET
-    - php: 7.3
-      env:
-        - DEPLOYMENT=SHARDED_CLUSTER
 
 before_install:
   - pip install "mongo-orchestration>=0.6.7,<1.0" --user `whoami`