stop clover instrumentation tasks being triggered during shadowJar build

Looks like one of JAL-3783,JAL-4110,JAL-4298 has resulted in a change in the task dependency graph for shadowJar. Regardless of the setting of 'clover', the gradle build always tries to execute clover related tasks. Judicious addition of -x can suppress them.

The shadowJar itself does not appear to include the instrumented classes or need clover jars to run, so this is not a bug in the code, just an undesirable issue with the build system.

gradle clean shadowJar --dry-run

> Configure project :
Using properties from file './utils/channels/default/channel_gradle.properties'
JALVIEW_VERSION is set to '2.11.3.0'
HEADLESS BUILD
J2S ENABLED
Using a LOCAL profile.
:clean SKIPPED
:copyHelp SKIPPED
:buildIndices SKIPPED
:copyResources SKIPPED
:copyChannelResources SKIPPED
:createBuildProperties SKIPPED
:buildResources SKIPPED
:copyDocs SKIPPED
:convertMdFiles SKIPPED
:releasesTemplates SKIPPED
:prepare SKIPPED
:compileJava SKIPPED
:processResources SKIPPED
:classes SKIPPED
:cleanClover SKIPPED
:cloverInstrJava SKIPPED
:cloverInstrTests SKIPPED
:cloverInstr SKIPPED
:compileCloverJava SKIPPED
:processCloverResources SKIPPED
:cloverClasses SKIPPED
:compileTestJava SKIPPED
:cleanPackageDir SKIPPED
:compileLinkCheck SKIPPED
:linkCheck SKIPPED
:jar SKIPPED
:syncJars SKIPPED
:makeDist SKIPPED
:processTestResources SKIPPED
:testClasses SKIPPED
:shadowJar SKIPPED