Allow both SpEL and property placeholder expressions to be used in the locators/servers attributes of the <gfe:pool> XML namespace element.

Currently, the <gfe:pool> element's, locators and servers attributes do not support the use of SpEL expressions (in addition to the currently supported Spring property placeholders) for configuration.

This JIRA will track the development of new Spring container infrastructure components to handle both Spring property placeholders and SpEL expressions in SDG's XML namespace, specifically for GemFire Pool bean definitions, using the XML namespace to configure GemFire.

My current thinking is... rather than include a lot of complex parsing logic in SDG's PoolParser to recognize and distinguish placeholder expressions (SpEL or property placeholders) from "actual values", to use a Spring's Type Conversion framework instead. In that way, Spring's container can properly evaluate the expression specified by the user and SDG can convert the evaluated value (most likely, a String) into a proper type (i.e. ConnectionEndpoint, or an array/collection of ConnectionEndpoints, a.k.a. ConnectionEndpointList).