Support nested expressions in deployment descriptors

Deployment descriptor aspect of WFCORE-179.

Users have requested support for expressions such as:

${VAULT::oracle::${me}::0}

where "me" is a system property.

Allows externalization of the vault attribute name.

This will likely require JBMETA changes as well, as the deployment level stuff is there.

I want this to be a generic thing, not just a specific solution to the above example. So, something like, given a string, find the innermost expression, resolve it and then repeat until the input equals the output (i.e. there are no more expressions.)