Use shared variant of dep for packaging

For native modules that have both static and shared variants (e.g.
cc_library), the deps mutator of android_filesystem would always create
a dep to the static variant. This is likely due to the fact that
`AddFarVariationDependencies` creates a dependency on the first variant
of the dep which matches the requested variations. `static` appears
before `shared` in linkMutator, and therefore android_filesystem would
always create a dep to the static variant.

This CL uses `OtherModuleFarDependencyVariantExists` to create a dep to
the shared variant. If a cc_library is listed in `PRODUCT_PACKAGES`, it
always means the shared variant.

Test: go test./filesystem
Test: diff in kati install files of vendor/ before and after this CL
https://diff.googleplex.com/#key=qrY73chVkwff

Change-Id: Iea9d6fde199ef95d43da2c041e2f84e5a7951285
diff --git a/android/packaging.go b/android/packaging.go
index d615871..b505964 100644
--- a/android/packaging.go
+++ b/android/packaging.go
@@ -377,7 +377,17 @@
 			if p.IgnoreMissingDependencies && !ctx.OtherModuleExists(dep) {
 				continue
 			}
-			ctx.AddFarVariationDependencies(t.Variations(), depTag, dep)
+			targetVariation := t.Variations()
+			sharedVariation := blueprint.Variation{
+				Mutator:   "link",
+				Variation: "shared",
+			}
+			// If a shared variation exists, use that. Static variants do not provide any standalone files
+			// for packaging.
+			if ctx.OtherModuleFarDependencyVariantExists([]blueprint.Variation{sharedVariation}, dep) {
+				targetVariation = append(targetVariation, sharedVariation)
+			}
+			ctx.AddFarVariationDependencies(targetVariation, depTag, dep)
 		}
 	}
 }