Pull swift-dispersion-populate to its own module

Related-Change: Ifcc8138e7b55d5b82bea0d411ec6bfcca2c77c83
Change-Id: I7f479359f94f102414f30e8aac87f377d10d34ee

setup.cfg

@@ -47,7 +47,6 @@ scripts =
     bin/swift-config
     bin/swift-container-info
     bin/swift-reconciler-enqueue
-    bin/swift-dispersion-populate
     bin/swift-drive-audit
     bin/swift-get-nodes
     bin/swift-object-info
@@ -79,6 +78,7 @@ console_scripts =
     swift-container-sharder = swift.container.sharder:main
     swift-container-sync = swift.container.sync:main
     swift-container-updater = swift.container.updater:main
+    swift-dispersion-populate = swift.cli.dispersion_populate:main
     swift-dispersion-report = swift.cli.dispersion_report:main
     swift-form-signature = swift.cli.form_signature:main
     swift-init = swift.common.manager:main