Disable build for commits pushed on master (#6804)

Fixes #6746.

Every commit on master is always the result of a merged PR, that has been tested by Travis. So retesting the merge commit on master is superfluous. This PR uses build conditions to avoid to launch a build for a commit push on master.

I also added the equivalent logic for AppVeyor. Builds cannot received conditions, so it needs to be done on init using Exit-AppVeyorBuild. This command does not fail the build, it finishes it prematurely with success.

* Disable build for commit pushed on master (PR are still tested of course)

* Equivalent exclusion code for AppVeyor

.travis.yml

@@ -18,6 +18,11 @@ branches:
     - /^\d+\.\d+\.x$/
     - /^test-.*$/
 
+# Since master can receive only commits from PR that have already been tested, we avoid with the
+# the following condition to launch again a pipeline when the merge commit is pushed to master.
+# However master still needs to be set in branches section to allow PR for master to be built.
+if: NOT (type = push AND branch = master)
+
 matrix:
   include:
     # These environments are always executed

appveyor.yml

@@ -11,6 +11,14 @@ branches:
     - /^\d+\.\d+\.x$/ # Version branches like X.X.X
     - /^test-.*$/
 
+init:
+  # Since master can receive only commits from PR that have already been tested, we avoid with the
+  # the following condition to launch again a pipeline when the merge commit is pushed to master.
+  # However master still needs to be set in branches section to allow PR for master to be built.
+  - ps: |
+      if (-Not $Env:APPVEYOR_PULL_REQUEST_NUMBER -And $Env:APPVEYOR_REPO_BRANCH -Eq 'master')
+      { $Env:APPVEYOR_SKIP_FINALIZE_ON_EXIT = 'true'; Exit-AppVeyorBuild }
+
 install:
   # Use Python 3.7 by default
   - "SET PATH=C:\\Python37;C:\\Python37\\Scripts;%PATH%"