HV-1809 Disable parallel test execution in the tck-runner following the TestNG upgrade

There seem to be problems with running tests in parallel with TestNG 6.14:
we end up with archive content being mixed between threads,
which leads to really cryptic errors in the SecurityManager (because we
try to load a resource when we shouldn't have... ?).
Anyway, the tests don't take that long to execute, so let's avoid this
source of errors?

Author: yrodiere

tck-runner/pom.xml

@@ -156,8 +156,6 @@
                             <value>${validation.provider}</value>
                         </property>
                     </systemProperties>
-                    <parallel>methods</parallel>
-                    <threadCount>4</threadCount>
                 </configuration>
             </plugin>
             <plugin>