gradle listExtensions displays mvn instructions
**Describe the bug**
In a project generated with Gradle, run `gradle listExtensions`. You should see in the end the following message: 

```
To get more information, append -Dquarkus.extension.format=full to your command line.

Add an extension to your project by adding the dependency to your project or use `mvn quarkus:add-extension -Dextensions="artifactId"`
```

**Expected behavior**
The message should be: 
```
To get more information, append <something> to your command line.

Add an extension to your project by adding the dependency to your project or use `gradle addExtension --extensions="artifactId"`
```

**Actual behavior**
It is not


**To Reproduce**
Steps to reproduce the behavior:
1. 
```
mvn io.quarkus:quarkus-maven-plugin:999-SNAPSHOT:create -DprojectGroupId=org.acme -DprojectArtifactId=foo -DclassName="org.acme.quickstart.GreetingResource" -Dpath="/hello" -Dextensions="resteasy" -DbuildTool=gradle
```
2. `cd foo & ./gradlew listExtensions`

**Environment (please complete the following information):**
 - Output of `uname -a` or `ver`: 
```
Linux ggastald-laptop 5.3.6-200.fc30.x86_64 #1 SMP Mon Oct 14 13:11:01 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
```
 - Output of `java -version`: 
```
openjdk version "1.8.0_212"
OpenJDK Runtime Environment (AdoptOpenJDK)(build 1.8.0_212-b03)
OpenJDK 64-Bit Server VM (AdoptOpenJDK)(build 25.212-b03, mixed mode)
```
 - GraalVM version (if different from Java):  unused
 - Quarkus version or git rev: master

**Additional context**

The stacktrace shown in the beginning is already covered in #4705

diff --git a/independent-projects/tools/common/src/main/java/io/quarkus/cli/commands/ListExtensions.java b/independent-projects/tools/common/src/main/java/io/quarkus/cli/commands/ListExtensions.java
index bcbd5c86433..96baee635ac 100644
--- a/independent-projects/tools/common/src/main/java/io/quarkus/cli/commands/ListExtensions.java
+++ b/independent-projects/tools/common/src/main/java/io/quarkus/cli/commands/ListExtensions.java
@@ -16,6 +16,7 @@
 import org.apache.maven.model.Dependency;
 
 import io.quarkus.cli.commands.file.BuildFile;
+import io.quarkus.cli.commands.file.GradleBuildFile;
 import io.quarkus.dependencies.Extension;
 
 public class ListExtensions {
@@ -63,11 +64,22 @@ public void listExtensions(boolean all, String format, String search) throws IOE
             loadedExtensions.forEach(extension -> display(extension, installed, all, currentFormatter));
 
             if ("concise".equalsIgnoreCase(format)) {
-                System.out.println("\\nTo get more information, append -Dquarkus.extension.format=full to your command line.");
+            	if (this.buildFile instanceof GradleBuildFile) {
+            		System.out.println("\\nTo get more information, append --format=full to your command line.");
+            	}
+            	else {
+            		System.out.println("\\nTo get more information, append -Dquarkus.extension.format=full to your command line.");
+            	}
             }
 
-            System.out.println("\\nAdd an extension to your project by adding the dependency to your " +
-                    "project or use `mvn quarkus:add-extension -Dextensions=\\"artifactId\\"`");
+            if (this.buildFile instanceof GradleBuildFile) {
+            	System.out.println("\\nAdd an extension to your project by adding the dependency to your " +
+                        "build.gradle or use `./gradlew addExtension --extensions=\\"artifactId\\"`");
+            }
+            else {
+            	System.out.println("\\nAdd an extension to your project by adding the dependency to your " +
+                        "pom.xml or use `./mvnw quarkus:add-extension -Dextensions=\\"artifactId\\"`");
+            }
         }
     }
 
['independent-projects/tools/common/src/main/java/io/quarkus/cli/commands/ListExtensions.java']