travis: move test invocation to script

Also restore set +e at end of the script.
cf. travis-ci/travis-ci#6307

Otherwise OSX builds fail at the end with:
  /Users/travis/.travis/job_stages: line 166: shell_session_update: command not found

Author: daviddrysdale

.travis.yml

@@ -108,6 +108,4 @@ install:
  - pip2 install --user --upgrade -r python/requirements.txt
 
 script:
- - getconf _NPROCESSORS_ONLN
- - ${MAKE} -j$(getconf _NPROCESSORS_ONLN) check VERBOSE=1 V=${ENV_VERBOSE}
- - ${MAKE} -C python test
+ - ./build/runtests.sh

build/runtests.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+set -e
+getconf _NPROCESSORS_ONLN
+${MAKE} -j$(getconf _NPROCESSORS_ONLN) check VERBOSE=1 V=${ENV_VERBOSE}
+${MAKE} -C python test
+set +e