Change the default dist_group from "android" to "unknown" to prevent
accidentally including java_sdk_library stubs that do not set
dist_group or owner in the public SDK.
Bug: 186723288
Test: TestJavaSdkLibraryDist
Change-Id: I9aae2a16254ac1a8d444acfa63bc571d1ef4b045
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