<clover-retarget/>, clove2r:retarget to change instrumentation settings without requiring a rebuild

We need to allow customers to change the initstring in their jars/wars/ear files after build them to make it easier for Clovered applications to be deployed in heterogeonous environments. Use of the clover.initstring system property is not good enough as often people don't have the ability to modify system properties.

Here's an example of where it's needed: https://support.atlassian.com/browse/CLV-4827?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel