cache downloaded zips fetched as part of building aggregate site for reuse across Jenkins slaves (rather than in each slave's workspace)

(2013-04-12 12:19:29) mistria: nickboldt: aggregate could compare logs
(2013-04-12 12:19:35) nickboldt: mistria: which logs?
(2013-04-12 12:20:58) mistria: nickboldt: the one we generate when using "fetch-zips"
(2013-04-12 12:22:40) nickboldt: so you want the aggregate job to fetch the zips BEFORE it builds the update site to determine if it should build the update site?
(2013-04-12 12:24:05) nickboldt: whole point of a "should I build?" check is that it happens before the build... eg., check SVN, check git, or run jbosstools-composite-install_master to check the installed IUs installed from the composite to determine if contents or versions have changed
(2013-04-12 12:24:46) nickboldt: not adverse to the idea of splitting the "fetch zips" step out of the "build aggregate" job, but ... then we have 2 more jobs to worry about
(2013-04-12 12:24:53) mistria: nickboldt: actually, the new version of the fetch mojo won't re-fetch zips if it finds out the the signature of the to-be-downloaded zip is the same as the one it has in cache
(2013-04-12 12:25:05) nickboldt: cache in workspace?
(2013-04-12 12:25:06) mistria: nickboldt: so no change, not fetch
(2013-04-12 12:25:23) nickboldt: or in static jenkins share folder?
(2013-04-12 12:25:23) mistria: nickboldt: in aggregate/site/zips
(2013-04-12 12:25:36) nickboldt: great, so it's one fetch per slave
(2013-04-12 12:26:14) nickboldt: would be better to cache that outside the workspace, if building in Jenkins
(2013-04-12 12:26:16) mistria: nickboldt: right, we should provide a way to override this directory and put in in a shared folder
(2013-04-12 12:27:12) mistria: nickboldt: there is not system property for that yet... https://github.com/jbosstools/jbosstools-maven-plugins/blob/master/tycho-plugins/repository-utils/src/main/java/org/jboss/tools/tycho/sitegenerator/FetchZipsFromRepo.java#L60
(2013-04-12 12:28:21) nickboldt: Old way: https://github.com/jbosstools/jbosstools-build-sites/blob/jbosstools-4.1.0.Alpha2x/aggregate/build.xml#L510 and https://github.com/jbosstools/jbosstools-build-sites/blob/jbosstools-4.1.0.Alpha2x/aggregate/build.xml#L33 (but we still dumped to ${output.dir}/zips, not to {WORKINGDIR}/zips )
(2013-04-12 12:28:58) nickboldt: mistria: should allow caching files in Jenkins's static file tree for use across slaves

So, I guess all we need to do is expose outputFolder to be overridden when -Phudson is enabled.

	/**
* Location where to put zips
* @parameter default-value="${basedir}/zips"
*/
private File outputFolder;

We could even set the correct path in the parent pom's hudson profile so that it need not be set in all the various jobs.