Enable checkstyle rule to catch variables that hide fields

Enable the checkstyle "HiddenFields" rule and fix any issues
that it detects.  Suppress these violations for parameters
to setters and constructors.

Added support for the checkstyle comment suppression module
// CHECKSTYLE:OFF and //CHECKSTYLE:ON are now
supported.

Suppressed HiddenField checks for net.onrc.onos.core.packet.*
rather than fix them.  These APIs are designed to
require formal parameters and local members having
the same name.

Change-Id: Ibc057603a934842d9c9b9b668f55bc5f5519e7f6
diff --git a/conf/checkstyle/onos_suppressions.xml b/conf/checkstyle/onos_suppressions.xml
index a32b222..9728687 100644
--- a/conf/checkstyle/onos_suppressions.xml
+++ b/conf/checkstyle/onos_suppressions.xml
@@ -12,6 +12,10 @@
     <suppress files="org.openflow.*" checks="[_a-zA-Z0-9]*"/>
     <suppress files="net.onrc.onos.core.datastore.serializers.*" checks="[_a-zA-Z0-9]*"/>
 
+    <!-- BigSwitch packet code is designed to use parameter names that override
+         local member names -->
+    <suppress files="net.onrc.onos.core.packet.*" checks="HiddenField"/>
+
     <suppress files=".*" checks="FinalParametersCheck"/>
     <suppress files=".*" checks="MagicNumbersCheck"/>
     <suppress files=".*" checks="DesignForExtensionCheck"/>