CI: Fail if PHP_FPM is set but not valid.

Author: notroj

test/travis_run_linux.sh

@@ -130,7 +130,7 @@ fi
 
 if test -v PHP_FPM; then
     # Sanity test the executable exists.
-    $PHP_FPM --version
+    $PHP_FPM --version || exit 1
 fi
 
 # Try to keep all potential coredumps from all processes