fix m2e NPE because of missing versionRange problem

eclipse's m2e plugin has a bug
https://bugs.eclipse.org/bugs/show_bug.cgi?id=347602
that causes it to throw an NPE if the versionRange
field is defined for a plugin.
The versionRange in dcache-core pom.xml was recently
removed with commit 6fe488be16de6a5e1ada58bba99a6f9f6f2c3645
because it caused maven to pull conflicting versions of
the datanucleus-maven-plugin.
This patch re-introduces the verionRange field, but uses
${datanucleus.plugin.version} instead of the open version
range used before.
This fixes the eclipse m2e while only pulling the version
defined in dache-parent.

Ticket:
Acked-by: Al
Acked-by: Paul
Target: master
Require-book: no
Require-notes: no