When running multiple builds, we frequently see failures due to port
conflicts, particularly with httpd tests. Retry with a different port
when the test function start_httpd() fails to reduce these spurious
failures.
We should not need to skip t9115-git-svn-dcommit-funky-renames as a
result. Remove it from GIT_SKIP_TESTS.
Similarly, adjust the git-daemon and svnserve start functions.
