Convert Split() calls with an equal sign to SplitN()

After seeing #7759, I decided to look at the calls in
Podman and Buildah to see if we had issues with strings.Split()
calls where an "=" (equals) sign was in play and we expected
to split on only the first one.

There were only one or two that I found in here that I think
might have been troubling, the remainder are just adding
some extra safety.

I also had another half dozen or so that were checking length
expectations appropriately, those I left alone.

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

libpod/image/filters.go

@@ -82,7 +82,7 @@ func LabelFilter(ctx context.Context, labelfilter string) ResultFilter {
 	// We need to handle both label=key and label=key=value
 	return func(i *Image) bool {
 		var value string
-		splitFilter := strings.Split(labelfilter, "=")
+		splitFilter := strings.SplitN(labelfilter, "=", 2)
 		key := splitFilter[0]
 		if len(splitFilter) > 1 {
 			value = splitFilter[1]
@@ -157,7 +157,7 @@ func (ir *Runtime) createFilterFuncs(filters []string, img *Image) ([]ResultFilt
 	var filterFuncs []ResultFilter
 	ctx := context.Background()
 	for _, filter := range filters {
-		splitFilter := strings.Split(filter, "=")
+		splitFilter := strings.SplitN(filter, "=", 2)
 		if len(splitFilter) < 2 {
 			return nil, errors.Errorf("invalid filter syntax %s", filter)
 		}