I have check out the master from Git, but couldn't build it. Not sure how (if at all) it succeeds on you build server. Anyway, these are the things I have changed to fix it (will send PR soon):

• Changed org.jboss.tools:parent:4.5.0.AM2-SNAPSHOT to 4.5.1.AM3-SNAPSHOT. (Otherwise it tried to download https://repository.jboss.org/nexus/content/repositories/snapshots/org/jboss/tools/targetplatforms/jbosstools-unified/4.70.0.AM1-SNAPSHOT/jbosstools-unified-4.70.0.AM1-SNAPSHOT-jbosstools-unified.target, which is HTTP 404. BTW, it still issues several warnings for not being able to retrieve the metadata, also directory of artifacts, like https://repository.jboss.org/nexus/content/repositories/snapshots/org/jboss/tools/parent give HTTP 500.)

• Increased project version from 1.5.300 to 1.5.301 (or else Tycho said org.jboss.ide.eclipse.freemarker: Only qualifier changed for (o
  rg.jboss.ide.eclipse.freemarker/1.5.300.v20170925-1612). "Expected to have bigger x.y.z than what is available in baseline (1.5.300.v20161214-1103)")