When starting the http service a given webapp is extracted into a working directory of the form: <host><port><context>. As part of shutdown this directory is cleaned up. However the directory is only completely removed when the JVM exits.
Occasionally subsequent tests will request to use the same port. This results in the same working directory being used. On Windows this will fail as the directory does not let itself be cleaned up before the webapp is redeployed to the same location as before.
We can randomize the working directory a bit more by adding a short sequence of random chars as part of the directory name.