Add option to exclude devtools from fat jar

Add an `excludeDevtools` property to both the Maven and Gradle plugin
that removes `org.springframework.boot:spring-boot-devtools` (if
necessary) when repackaging the application.

Closes gh-3171

spring-boot-docs/src/main/asciidoc/build-tool-plugins.adoc

@@ -395,6 +395,10 @@ want the other Boot features but not this one)
 |`embeddedLaunchScriptProperties`
 |Additional properties that to be expanded in the launch script. The default script
  supports a `mode` property which can contain the values `auto`, `service` or `run`.
+
+|`excludeDevtools`
+|Boolean flag to indicate if the devtools jar should be excluded from the repackaged
+archives. Defaults to `false`.
 |===
 
 

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -844,6 +844,10 @@ applied to other modules using your project. Gradle does not support `optional`
 dependencies out-of-the-box so you may want to have a look to the
 {propdeps-plugin}[`propdeps-plugin`] in the meantime.
 
+TIP: If you want to ensure that devtools is never included in a production build, you can
+use set the `excludeDevtools` build property to completely remove the JAR. The property is
+supported with both the Maven and Gradle plugins.
+
 
 
 [[using-boot-devtools-property-defaults]]