Get app cert hash from Play Store API and send it to IRDB

This is needed because IRDB contains information on Android apps that
aren't in the Play Store, and differentiates them by production
certificate SHA256 hash fingerprint.  So we need to know the value of
this hash in order to ask IRDB about links to/from a specific app,
which we can fortunately get by querying the Play Store.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125566907

javatests/google/registry/flows/FlowTestCase.java

@@ -298,7 +298,8 @@ public abstract class FlowTestCase<F extends Flow> {
       CommitMode commitMode, UserPrivileges userPrivileges, String xml, String... ignoredPaths)
       throws Exception {
     // Always ignore the server trid, since it's generated and meaningless to flow correctness.
-    String[] ignoredPathsPlusTrid = FluentIterable.from(ignoredPaths)
+    // TODO(user): Remove asList()
+    String[] ignoredPathsPlusTrid = FluentIterable.from(asList(ignoredPaths))
         .append("epp.response.trID.svTRID")
         .toArray(String.class);
     EppOutput output = runFlowInternal(commitMode, userPrivileges);