commit 19b593092ba533a9d3859737599ba1f4416c54cf
Author: Krunal Bauskar <krunal.bauskar@percona.com>
Date: Thu Mar 28 10:55:09 2019 +0530

• PXC#2491: SST is failing if the donor has encrypted undo logs.

• .7 doesn't support undo log encrpytion and has no plan
  to support it in future given that the implementation has been
  replaced in PS with MySQL native implementation.

• Infact, .7 don't plan to support any of these
  data-at-reset encryption features

• innodb_temp_tablespace_encrypt

• innodb_sys_tablespace_encrypt

• innodb_encrypt_tables

• innodb_parallel_dblwr_encrypt

• innodb_undo_log_encrypt

• innodb_redo_log_encrypt

• Support for existing features that .7 started supporting (BETA quality)
  general tablespace, file-per-table, encrypt-tmp-files will continue under
  BETA quality tag.

.7 only support general and file_per_table based encryption.

all other encryption is not supported by PXC.

So this scenario is invalid. But we should block user from setting it to avoid confusion.

I will block setting the said option in .7.