Add coverity scan, faster CI

.travis.yml

@@ -2,10 +2,9 @@ dist: bionic
 language: c
 before_install:
   - sudo apt-get -y --no-install-recommends install postgresql-10 postgresql-server-dev-10
-  - sudo service postgresql stop
+  - sudo pkill -9 postgres
   - echo -n | openssl s_client -connect https://scan.coverity.com:443 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' | sudo tee -a /etc/ssl/certs/ca-
 
-after_success:
 compiler:
   - clang
   - gcc