Update fuse target platform to point to DevStudio AM1 TP

Now that the AM1 DevStudio version for Oxygen has been updated, we need to update the Fuse target platform accordingly. This involves changing the coretests URL in fuse-jbosstools.target to point to http://download.jboss.org/jbosstools/oxygen/staging/updates/coretests/4.5.0.AM1/

This must be done here - https://github.com/jbosstools/jbosstools-fuse/blob/master/targetplatform/multiple/fuse-jbosstools.target#L47