HADOOP-17513. Checkstyle IllegalImport does not catch guava imports (#2678)

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-build-tools/src/main/resources/checkstyle/checkstyle.xml

@@ -121,7 +121,7 @@
         <!-- See http://checkstyle.sf.net/config_import.html -->
         <module name="IllegalImport">
           <property name="regexp" value="true"/>
-          <property name="illegalPkgs" value="^sun\.[^.]+, ^com\.google\.common\.[^.]+"/>
+          <property name="illegalPkgs" value="sun, com\.google\.common"/>
           <property name="illegalClasses" value="^org\.apache\.hadoop\.thirdparty\.com\.google\.common\.base\.(Optional|Function|Predicate|Supplier), ^org\.apache\.hadoop\.thirdparty\.com\.google\.common\.collect\.(ImmutableListMultimap)"/>
         </module>
         <module name="RedundantImport"/>