DATAREDIS-629 - Adopt changed Mono and Flux error handling API.

Replace Flux/Mono.onErrorResumeWith(…) with Flux/Mono.onErrorMap(…) and turn translateException into a method returning a mapping function instead of a reactive type emitting the mapped exception. Replace otherwiseIfEmpty(…) with switchIfEmpty(…) and otherwiseReturn(…) with onErrorReturn(…).

src/test/java/org/springframework/data/redis/connection/lettuce/LettuceReactiveKeyCommandsTests.java

@@ -110,7 +110,7 @@ public class LettuceReactiveKeyCommandsTests extends LettuceReactiveCommandsTest
 	}
 
 	@Test(expected = RedisSystemException.class) // DATAREDIS-525
-	public void renameShouldThrowErrorWhenKeyDoesNotExit() {
+	public void renameShouldThrowErrorWhenKeyDoesNotExist() {
 		assertThat(connection.keyCommands().rename(KEY_1_BBUFFER, KEY_2_BBUFFER).block(), is(true));
 	}