If the target symbolic link already existed, an invalid link in target
was created to java/target. Fixed by checking if the link exists before
creating it
Change-Id: I3ebcdcf0de1412838d78a2d2e647e265c41502e8
Also, pull and build monasca-common directly instead of using
jars from tarballs.openstack.org since zuul often gets backed
up and jars don't get updated fast enough
Change-Id: I27c964eb2b732c70c0e8c8d2b74b160c921e899d