Fixed broken tests

ReplicationDomain.java:
Made ieContext private and used an AtomicReference for it + In acquireIEContext() and releaseIEContext(), removed now useless synchronized keyword.
In acquireIEContext(), returned the created ieContext + changed all client code to assign a variable from the result.

ReplicationDomainTest.java:
Avoid NPE in case the ieContext is released before the asserts.
Called ReplicationDomain.getImportExportContext().