BUILD: CI: disable slow regtests on Travis

We're getting almost 100% failure rate recently due to the "slow" tests
never completing in time on Travis. Peers do not synchronize their data
within the expected delay, health checks time out due to the tested
agent not responding, etc. This adds a lot of noise and completely voids
the value of the build test.

Let's disable the slow tests to try to get back to a fully working state.

.travis.yml

@@ -112,7 +112,7 @@ script:
   - ./haproxy -vv
   - if [ "${TRAVIS_OS_NAME}" = "linux" ]; then ldd haproxy; fi
   - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then otool -L haproxy; fi
-  - env VTEST_PROGRAM=../vtest/vtest make reg-tests
+  - make reg-tests VTEST_PROGRAM=../vtest/vtest REGTESTS_TYPES=default,bug,devel
 
 after_failure:
   - |