Merge branch 'master' into allocation#27427-1

* master: (27 commits)
  Declare empty package dirs as output dirs
  Consistent updates of IndexShardSnapshotStatus (elastic#28130)
  Fix Gradle wrapper usage on Windows when building BWC (elastic#28146)
  [Docs] Fix some typos in comments (elastic#28098)
  Use Gradle wrapper when building BWC
  Painless: Add a simple cache for whitelist methods and fields. (elastic#28142)
  Fix upgrading indices which use a custom similarity plugin. (elastic#26985)
  Fix Licenses values for CDDL and Custom URL (elastic#27999)
  Cleanup TcpChannelFactory and remove classes (elastic#28102)
  Fix expected plugins test for transport-nio
  [Docs] Fix Date Math example descriptions (elastic#28125)
  Fail rollover if duplicated alias found in template (elastic#28110)
  Avoid concurrent snapshot finalizations when deleting an INIT snapshot (elastic#28078)
  Deprecate `isShardsAcked()` in favour of `isShardsAcknowledged()` (elastic#27819)
  [TEST] Wait for replicas to be allocated before shrinking
  Use the underlying connection version for CCS connections  (elastic#28093)
  test: do not use asn fields
  Test: Add assumeFalse for test that cannot pass on windows
  Clarify reproduce info on Windows
  Remove out-of-date projectile file
  ...

CONTRIBUTING.md

@@ -99,13 +99,13 @@ We support development in the Eclipse and IntelliJ IDEs. For Eclipse, the
 minimum version that we support is [Eclipse Oxygen][eclipse] (version 4.7). For
 IntelliJ, the minimum version that we support is [IntelliJ 2017.2][intellij].
 
-Eclipse users can automatically configure their IDE: `gradle eclipse`
+Eclipse users can automatically configure their IDE: `./gradlew eclipse`
 then `File: Import: Existing Projects into Workspace`. Select the
 option `Search for nested projects`. Additionally you will want to
 ensure that Eclipse is using 2048m of heap by modifying `eclipse.ini`
 accordingly to avoid GC overhead errors.
 
-IntelliJ users can automatically configure their IDE: `gradle idea`
+IntelliJ users can automatically configure their IDE: `./gradlew idea`
 then `File->New Project From Existing Sources`. Point to the root of
 the source directory, select
 `Import project from external model->Gradle`, enable
@@ -123,7 +123,7 @@ restart of IDEA). For IDEA 2017.3 and above, in addition to the JVM option, you
 classpath](https://github.com/elastic/elasticsearch/issues/14348) if that is
 reported as a source of jar hell.
 
-To run an instance of elasticsearch from the source code run `gradle run`
+To run an instance of elasticsearch from the source code run `./gradlew run`
 
 The Elasticsearch codebase makes heavy use of Java `assert`s and the
 test runner requires that assertions be enabled within the JVM. This
@@ -151,15 +151,15 @@ To create a distribution from the source, simply run:
 
 ```sh
 cd elasticsearch/
-gradle assemble
+./gradlew assemble
 ```
 
 You will find the newly built packages under: `./distribution/(deb|rpm|tar|zip)/build/distributions/`.
 
 Before submitting your changes, run the test suite to make sure that nothing is broken, with:
 
 ```sh
-gradle check
+./gradlew check
 ```
 
 Contributing as part of a class
@@ -187,7 +187,7 @@ code review process because it wastes our time.
 * We don't have the capacity to absorb an entire class full of new contributors,
 especially when they are unlikely to become long time contributors.
 
-Finally, we require that you run `gradle check` before submitting a
+Finally, we require that you run `./gradlew check` before submitting a
 non-documentation contribution. This is mentioned above, but it is worth
 repeating in this section because it has come up in this context.
 

README.textile

@@ -202,9 +202,9 @@ We have just covered a very small portion of what Elasticsearch is all about. Fo
 
 h3. Building from Source
 
-Elasticsearch uses "Gradle":https://gradle.org for its build system. You'll need to have at least version 3.3 of Gradle installed.
+Elasticsearch uses "Gradle":https://gradle.org for its build system.
 
-In order to create a distribution, simply run the @gradle assemble@ command in the cloned directory.
+In order to create a distribution, simply run the @./gradlew assemble@ command in the cloned directory.
 
 The distribution for each project will be created under the @build/distributions@ directory in that project.