Feature: Add key and encrypted value to failed decryption error message

Previously it would just say that it failed to decrypt a value, but wouldn't
give you any information on which one it was, so it was impossible to fix.

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Change-Id:     I1f3f92dc889cd3a901af66de57fd63a4ed2d380a
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>