Allow mvn verify load factor to be configured at the command line (#…

…3852)

Currently, if you run `mvn verify` you get the moral equivalent of `make
-j$(nproc)`; this isn't always desirable in CI where we might want a
smaller load factor to reduce contention on a machine.

This PR allows you to pass an option:
```
mvn verify -DcoreFactor=FACTOR
```
to set the number of cores used to the nearest positive integer to
`$(nproc) / FACTOR`.

Co-authored-by: rv-jenkins <[email protected]>

k-distribution/pom.xml

@@ -16,6 +16,7 @@
   <properties>
     <config>tests/config.xml</config>
     <ktestDir>${project.basedir}</ktestDir>
+    <coreFactor>1</coreFactor>
   </properties>
 
   <dependencies>
@@ -56,6 +57,9 @@
             <goals>
               <goal>cpu-count</goal>
             </goals>
+            <configuration>
+              <factor>${coreFactor}</factor>
+            </configuration>
           </execution>
         </executions>
       </plugin>