Support dist_group property instead of owner for setting sdk dist subdirectory

Reusing the owner property is confusing, especially when the property is
required on every java_sdk_library module.  Create a new dist_group property
to use instead.

Bug: 186723288
Test: TestJavaSdkLibraryDist
Change-Id: I9e62c703a95d6b63cafa60bffb1b37ba85388593
Merged-In: I9e62c703a95d6b63cafa60bffb1b37ba85388593
(cherry picked from commit 986b69aa)