make CF_HOME directory properly unique for each migrate_mysql_to_credhub invocation, and clean it up at the end [#162595262](https://www.pivotaltracker.com/story/show/162595262)
make CF_HOME directory properly unique for each migrate_mysql_to_credhub invocation, and clean it up at the end [#162595262](https://www.pivotaltracker.com/story/show/162595262)

cloudfoundry-incubator/nfs-volume-release,cloudfoundry-incubator/nfs-volume-release,cloudfoundry-incubator/nfs-volume-release