IMPALA-9008: Serialize Maven invocations to deflake query-event-hook-api

The previous commit for this Jira serialized the compilation of
shaded-deps and ext-data-source to fix flakiness. It looks like
this led to a new similar issue related to the parallel compilation
of ext-data-source and query-event-hook-api.

Similarly to the shaded-deps issue, I try to fix this by adding a
fictional dependency (query-event-hook-api -> yarn-extras) to serialize
the build.

Full Maven dependency graph:
fe -> query-event-hook-api -> yarn-extras -> ext-data-source ->
     shaded-deps-> impala-parent
The ordering of query-event-hook-apit, yarn-extras, ext-data-source,
and shaded-deps are arbitrary.

Change-Id: Ice0dfda5ee0ef60c9c208f05b0952555770fc090
Reviewed-on: http://gerrit.cloudera.org:8080/14423
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
Reviewed-by: Csaba Ringhofer <csringhofer@cloudera.com>
Tested-by: Csaba Ringhofer <csringhofer@cloudera.com>

query-event-hook-api/CMakeLists.txt

@@ -15,6 +15,8 @@
 # specific language governing permissions and limitations
 # under the License.
 
-add_custom_target(query-event-hook-api ALL DEPENDS gen-deps impala-parent
+# The dependency on yarn-extras is only added to avoid parallel downloads
+# of dependencies. For more details see IMPALA-7051, which was a similar issue.
+add_custom_target(query-event-hook-api ALL DEPENDS gen-deps impala-parent yarn-extras
   COMMAND $ENV{IMPALA_HOME}/bin/mvn-quiet.sh -B install -DskipTests
 )