[SPARK-18662] Move resource managers to separate directory

## What changes were proposed in this pull request?

* Moves yarn and mesos scheduler backends to resource-managers/ sub-directory (in preparation for https://issues.apache.org/jira/browse/SPARK-18278)
* Corresponding change in top-level pom.xml.

Ref: https://github.com/apache/spark/pull/16061#issuecomment-263649340

## How was this patch tested?

* Manual tests

/cc rxin

Author: Anirudh <ramanathana@google.com>

Closes #16092 from foxish/fix-scheduler-structure-2.

dev/sparktestsupport/modules.py

@@ -469,7 +469,7 @@ yarn = Module(
     name="yarn",
     dependencies=[],
     source_file_regexes=[
-        "yarn/",
+        "resource-managers/yarn/",
         "common/network-yarn/",
     ],
     build_profile_flags=["-Pyarn"],
@@ -485,7 +485,7 @@ yarn = Module(
 mesos = Module(
     name="mesos",
     dependencies=[],
-    source_file_regexes=["mesos/"],
+    source_file_regexes=["resource-managers/mesos/"],
     build_profile_flags=["-Pmesos"],
     sbt_test_goals=["mesos/test"]
 )

pom.xml

@@ -2580,7 +2580,7 @@
     <profile>
       <id>yarn</id>
       <modules>
-        <module>yarn</module>
+        <module>resource-managers/yarn</module>
         <module>common/network-yarn</module>
       </modules>
     </profile>
@@ -2588,7 +2588,7 @@
     <profile>
       <id>mesos</id>
       <modules>
-        <module>mesos</module>
+        <module>resource-managers/mesos</module>
       </modules>
     </profile>
 

mesos/pom.xml → resource-managers/mesos/pom.xml

@@ -21,7 +21,7 @@
     <groupId>org.apache.spark</groupId>
     <artifactId>spark-parent_2.11</artifactId>
     <version>2.2.0-SNAPSHOT</version>
-    <relativePath>../pom.xml</relativePath>
+    <relativePath>../../pom.xml</relativePath>
   </parent>
 
   <artifactId>spark-mesos_2.11</artifactId>