Properly handle Yaws installation if a previous version already exists

From version 1.99, /usr/lib/yaws is a symlink on
/usr/lib/erlang/lib/yaws-{VSN}. In previous versions, this was a directory. So
we must remove this directory to create the symlink at the right place.

Because this directory can contain user data, we rename it instead of removing
it.
Fix regular-install script by using $(logdir) variable
Do not use hostname to generate default yaws configuration

Fix issue #191
Do not test Yaws anymore on R14B02 on Travis platform

It seems that we hit the bug OTP-9214 on Travis. This has worked in the
past. But now, for an unknown reason, the testsuite fails on R14B02 because of
this bug.
Show report.log if yaws is not started during a test
Fix commit adb3c360