rust: Allow rust_tests to include data files.

Adds the ability to define data files that should be installed alongside
the test.

This also fixes a bug wherein rust_test properties were duplicated.

Bug: 171710847
Test: rust_test module with "data" property installs files to device.
Change-Id: I091489afaf7e76b751a33a28049590d9fb39fe5f

rust/rust_test.go

@@ -116,6 +116,7 @@ func (tctx *testRustCtx) useMockedFs() {
 		"foo.proto":       nil,
 		"liby.so":         nil,
 		"libz.so":         nil,
+		"data.txt":        nil,
 	}
 }