Adressed PR comments

Author: fernst

src/test/java/io/cdap/plugin/gcp/bigquery/util/BigQueryUtilTest.java

@@ -169,7 +169,7 @@ public void testGetBucketPrefixInvalidBucketName() {
     SettableArguments args = Mockito.mock(SettableArguments.class);
     Mockito.when(args.has(BUCKET_PREFIX_ARG))
       .thenReturn(true);
-    Mockito.when(args.get("io.cdap.plugin.bigquery.bucket.prefix"))
+    Mockito.when(args.get(BUCKET_PREFIX_ARG))
       .thenReturn("This is an invalid bucket name!@");
 
     IllegalArgumentException e = null;
@@ -191,7 +191,7 @@ public void testGetBucketPrefixTooLong() {
     SettableArguments args = Mockito.mock(SettableArguments.class);
     Mockito.when(args.has(BUCKET_PREFIX_ARG))
       .thenReturn(true);
-    Mockito.when(args.get("io.cdap.plugin.bigquery.bucket.prefix"))
+    Mockito.when(args.get(BUCKET_PREFIX_ARG))
       .thenReturn("this-prefix-is-too-long-to-be-used-as-a-prefix-oops");
 
     IllegalArgumentException e = null;