XD-1221 Remove build task from modules project

This avoids 'build' directory created under 'modules'

Currently, the 'modules' project is considered as JavaProject
and the build task creates a 'build' directory which gets copied into
the dist as well. Rather than removing the 'build' directory from
modules subproject during 'dist', it is better to disable build task
for 'modules' project as it simply acts as a wrapper around the individual
modules.

The only reason modules project is considered as JavaProject is to
enable the eclipse/idea plugins to generate metadata.
XD-1222 Remove duplicate MBeanServer def

https://jira.springsource.org/browse/XD-1222
Since the 'jmxEnabled' flag is shared by admin/launcher and
the module's MBeanExportingPlugin, the definition of MBeanServer
by the module's plugin becomes duplicate as the MBeanServer
is already defined as XD global beans (xd-global-beans.xml)
validation-api compile rather than testCompile dep