[performance tuning] create separate jbosstools-nightly-staging-composite site for SOA Tooling

To speed up SOA Tooling aggregate build, source from a new URL instead of http://download.jboss.org/jbosstools/builds/staging/_composite_/trunk/. This would mean no metadata for content that will ultimately not be included in the site will be downloaded – only metadata for staged SOA nightlies will be read/used.

1. create new site http://download.jboss.org/jbosstools/builds/staging/_composite_/soa/trunk/ or similar (need two sites for use with trunk and stable_branch)

2. Add new propert(ies) to parent pom.xml (to complement jbosstools-nightly-staging-composite)

3. Replace reference to jbosstools-nightly-staging-composite in build/aggregate/soa-site/pom.xml with new URL

4. Ensure that build/aggregate/soa-site/pom.xml can find published URL of correct nightly JBT Core site (for trunk or stable_branch), eg., http://download.jboss.org/jbosstools/updates/nightly/core/trunk/ or http://download.jboss.org/jbosstools/updates/nightly/core/3.3.indigo/ – needed to resolve dependencies to common components in JBT Core or the SOA site won't be able to build/resolve/get installed.

5. respin to verify