Travis CI: conditionally skip some tests

Based on Claudio's changes proposed in openwall#4484

Author: solardiz

.travis.yml

@@ -1,7 +1,8 @@
 language: c
 dist: bionic
+os: linux
 
-matrix:
+jobs:
   include:
 
   # #### CPU formats test (gcc)
@@ -57,15 +58,5 @@ matrix:
     osx_image: xcode9.4
     env: OPENCL="yes"
 
-  # #########################################
-  # #### Extra Testing Scheme
-  # #########################################
-
-  # #### Intel OpenCL runtime Docker based testing
-  - if: branch = bleeding-jumbo AND env(TRAVIS_PULL_REQUEST) = false
-    os: linux
-    compiler: gcc
-    env: DOCKER="yes" OPENCL="yes"
-
 script:
   - .travis/travis-ci.sh

.travis/travis-ci.sh

@@ -1,5 +1,23 @@
 #!/bin/bash
 
+# if requested, run all tests
+if [[ "$TRAVIS_PULL_REQUEST_BRANCH" != "force-travis" ]]; then
+
+    # on the main branch, run all tests
+    if [[ "$TRAVIS_BRANCH" != "bleeding-jumbo" || "$TRAVIS_PULL_REQUEST" =~ ^[0-9]+$ ]]; then
+
+#        # otherwise, run only Linux jobs for now
+#        if [[ "$TRAVIS_OS_NAME" != "linux" ]]; then
+            echo '---------------------------------- Skipping CI ---------------------------------'
+            echo 'In order to spare resources, skip Travis CI build.'
+            echo '--------------------------------------------------------------------------------'
+
+            # Nothing to do.
+            exit 0
+#        fi
+    fi
+fi
+
 # Need a docker image to run the tests
 if [[ "$DOCKER" == "yes" ]]; then
     docker run --cap-add SYS_PTRACE -v "$(pwd)":/cwd claudioandre/john:opencl sh -c \