test/travis_before_linux.sh: make for loop more resilient

test/travis_before_linux.sh: make for loop more resilient

This is a follow up to my last commit to this file, to make
the for loop more resilient with the following:
- use --force in svn export, otherwise the second attempt will
  always fail due to the dest directory already present.
- exit 1 in case the 5 tries end up in a non zero exit code
  (to fail fast the build).

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1872045 13f79535-47bb-0310-9956-ffa450edef68