Rename all testdata loading files to conform to a single naming scheme

The scheme is:
- loadBytes: returns a ByteSource of the data
- loadFile: returns a string using UTF8 encoding, optionally applying
  substitutions

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177606406

javatests/google/registry/tools/AllocateDomainCommandTest.java

@@ -104,7 +104,7 @@ public class AllocateDomainCommandTest extends CommandTestCase<AllocateDomainCom
             .setClientId("NewRegistrar")
             .setModificationTime(application.getCreationTime())
             .setTrid(Trid.create("ABC-123", "server-trid"))
-            .setXmlBytes(ToolsTestData.get(xmlFile).read())
+            .setXmlBytes(ToolsTestData.loadBytes(xmlFile).read())
             .build());
   }
 
@@ -149,7 +149,7 @@ public class AllocateDomainCommandTest extends CommandTestCase<AllocateDomainCom
 
   @Test
   public void testXmlInstantiatesFlow() throws Exception {
-    byte[] xmlBytes = ToolsTestData.get("allocate_domain.xml").read();
+    byte[] xmlBytes = ToolsTestData.loadBytes("allocate_domain.xml").read();
     assertThat(getFlowClass(unmarshal(EppInput.class, xmlBytes)))
         .isEqualTo(DomainAllocateFlow.class);
   }