modify reconciler to use new Delta() compare

Updates the ACK runtime and type system to use the new
`pkg/compare.Delta` comparison functionality. The
`AWSResourceDescriptor.Diff()` and `AWSResourceDescriptor.Equal()`
methods were removed and replaced with a single
`AWSResourceDescriptor.Delta()` method that returns a
`*pkg/compare.Delta` struct containing the difference between two
objects under comparison.

A corresponding patch to the
github.com/aws-controllers-k8s/code-generator repository adds the
generation of the `newResourceDelta()` resource package-local function
that recurses into an object and compares the fields in the objects to
each other.

Included in this patch is an update to the `mocks` Makefile target which
now builds mocks for `k8s.io/apimachinery` interfaces that we use in a
new unit test of the update code path in the reconciler.

In order to adhere to best practices of only using exported functions in
Go module testing, I ended up exporting the
`pkg/runtime.reconciler.sync()` method as a `Sync()` method on the
`AWSResourceReconciler` interface. The unit test features a whole lot of
mock setups and definitely could use some refactoring to reduce the
number of setup mocks needed.

IMPORTANT! This is a BREAKING change to the runtime interfaces. Once
merged, we will need to cut a new Git release to signal to consumers
that this is a backwards-incompatible change and if they attempt to
regenerate their controllers with the new code and their controllers
rely on the older interfaces that uses a "diffReporter" struct, they
will generate broken code.

Author: jaypipes

Makefile

@@ -1,7 +1,9 @@
 SHELL := /bin/bash # Use bash syntax
 
-# Set up variables
+GOPATH ?= "$(HOME)/go"
 GO111MODULE=on
+K8S_APIMACHINERY_VERSION = $(shell go list -m -f '{{ .Version }}' k8s.io/apimachinery)
+K8S_APIMACHINERY_DIR = "$(GOPATH)/pkg/mod/k8s.io/apimachinery@$(K8S_APIMACHINERY_VERSION)"
 
 .PHONY: all test clean-mocks mocks
 
@@ -20,6 +22,15 @@ mocks: install-mockery ## Build mocks
 	@echo -n "building mocks for pkg/types ... "
 	@bin/mockery --quiet --all --tags=codegen --case=underscore --output=mocks/pkg/types --dir=pkg/types
 	@echo "ok."
+	@echo -n "building mocks for k8s.io/apimachinery/pkg/apis/meta/v1 ... "
+	@bin/mockery --quiet --name=Object --case=underscore --output=mocks/apimachinery/pkg/apis/meta/v1 --dir="$(K8S_APIMACHINERY_DIR)/pkg/apis/meta/v1"
+	@echo "ok."
+	@echo -n "building mocks for k8s.io/apimachinery/runtime ... "
+	@bin/mockery --quiet --name=Object --case=underscore --output=mocks/apimachinery/pkg/runtime --dir="$(K8S_APIMACHINERY_DIR)/pkg/runtime"
+	@echo "ok."
+	@echo -n "building mocks for k8s.io/apimachinery/runtime/schema ... "
+	@bin/mockery --quiet --name=ObjectKind --case=underscore --output=mocks/apimachinery/pkg/runtime/schema --dir="$(K8S_APIMACHINERY_DIR)/pkg/runtime/schema"
+	@echo "ok."
 
 help:           ## Show this help.
 	@grep -F -h "##" $(MAKEFILE_LIST) | grep -F -v grep | sed -e 's/\\$$//' \