Implement --remote_force_print_messages

Adds a flag for always printing messages returned by remotely executed
actions.

src/main/java/com/google/devtools/build/lib/remote/RemoteSpawnRunner.java

@@ -274,7 +274,7 @@ public SpawnResult exec(Spawn spawn, SpawnExecutionContext context)
 
             FileOutErr outErr = context.getFileOutErr();
             String message = result.getMessage();
-            if (!result.success() && !message.isEmpty()) {
+            if ((!result.success() || remoteOptions.remoteForcePrintMessages) && !message.isEmpty()) {
               outErr.printErr(message + "\n");
             }
 

src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java

@@ -574,6 +574,17 @@ public RemoteOutputsStrategyConverter() {
       help = "Maximum number of open files allowed during BEP artifact upload.")
   public int maximumOpenFiles;
 
+  @Option(
+      name = "remote_force_print_messages",
+      defaultValue = "false",
+      category = "remote",
+      documentationCategory = OptionDocumentationCategory.LOGGING,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      help =
+          "If set to true, Bazel will always print messages returned by remotely executed actions. "
+              + "By default these messages are only printed for failing actions.")
+  public boolean remoteForcePrintMessages;
+
   // The below options are not configurable by users, only tests.
   // This is part of the effort to reduce the overall number of flags.