Enable the max effort and low threshold by default.

This change makes the default configuration of FindBugs much more paranoid.
On the Low level there are many Not-important issues, but experience of jenkinsci/envinject-lib#13 shows that otherwise we may miss real NPE risks in Jenkins.

pom.xml

@@ -65,6 +65,10 @@
     <!-- Whether the build should fail if findbugs finds any error. -->
     <!-- It is strongly encouraged to leave it as true. Use false with care only in transient situations. -->
     <findbugs.failOnError>true</findbugs.failOnError>
+    <!-- Defines a default FindBugs threshold. -->
+    <!-- In Plugin POM 2.x the default value was Medium, but it was not enough to discover some null handling cases -->
+    <findbugs.threshold>Low</findbugs.threshold>
+
     <!-- Whether to skip tests during release phase (they are executed in the prepare phase). -->
     <release.skipTests>true</release.skipTests>
     <!-- By default we do not create *-tests.jar. Set to false to allow other plugins to depend on test utilities in yours, using <classifier>tests</classifier>. -->
@@ -566,6 +570,8 @@
               <!--  Instead we configure this in a profile -->
               <xmlOutput>true</xmlOutput>
               <findbugsXmlOutput>false</findbugsXmlOutput>
+              <effort>Max</effort>
+              <threshold>${findbugs.threshold}</threshold>
             </configuration>
           </execution>
         </executions>