XDCR log keys as binary array and operation is wrong

While debugging MB-42352 I saw this issue:

Problem
XDCR logs the key as binary array [116 101 115 116] and the operation is wrong setMeta. The operation in question here is a delete_with_meta

2020-10-29T16:44:48.605Z ERRO GOXDCR.XmemNozzle: xmem_84576cb22c4dd3a9bd354e17b2186eec/test/test_10.112.205.101:11210_0 received error response from setMeta client. Repairing connection. response status=EINVAL, opcode=0xa8, seqno=1, req.Key=<ud>[116 101 115 116]</ud>, req.Cas=0, req.Extras=[0 0 0 0 95 154 227 170 0 0 0 0 0 0 0 2 22 66 126 225 139 162 0 0]

Steps to Reproduce

1. Create a document that expiries in 10 seconds with user xattrs

   /opt/couchbase/bin/cbc-subdoc -U couchbase://localhost/test -u Administrator -P password

   subdoc> set test value -x xattr=100 -e 10

   2. Wait 10 seconds
   3. Setup XDCR where the target cluster is 6.6.0.
   4. XDCR will fail because of MB-42352 and the log message above is produce

Expectation

For the log message to have the key as a string and for the opcode being used to be correct.

For example:

2020-10-29T16:44:48.605Z ERRO GOXDCR.XmemNozzle: xmem_84576cb22c4dd3a9bd354e17b2186eec/test/test_10.112.205.101:11210_0 received error response from Meta client. Repairing connection. response status=EINVAL, opcode=0xa8, seqno=1, req.Key=<ud>test</ud>, req.Cas=0, req.Extras=[0 0 0 0 95 154 227 170 0 0 0 0 0 0 0 2 22 66 126 225 139 162 0 0]