cbbackupmgr crashes with "fatal error: concurrent map read and map write"

./opt/couchbase/bin/cbbackupmgr config --archive /workspace/backup --repo default

./opt/couchbase/bin/cbbackupmgr backup --archive /workspace/backup --repo default  --threads 16 --host http://172.23.132.17:8091 --username Administrator --password password

CHANGELOG for backup

 * Commit: b4fdd8bf8b484ec344cb421bf5562e27ddc8fa90 (in build: 2276)

   Author: Mike Wiederhold

   Add a way to get the persisted vbucket seqno ranges for a backup

   Change-Id: Iefd5566feb4496cb10813b1f5bd3940bc9659327

   Reviewed-on: http://review.couchbase.org/74967

   Reviewed-by: Michael Wiederhold 

   Tested-by: Michael Wiederhold 

 * Commit: 084cc218bd3e6411cf82832a4b27a12ba546ad49 (in build: 2276)

   Author: Mike Wiederhold

   MB-23205: Make merge work we the purge seqno causes a rollback

   Change-Id: I8cc401be6c6845482e176061c69d0058982467e0

   Reviewed-on: http://review.couchbase.org/74968

   Reviewed-by: Michael Wiederhold 

   Tested-by: Michael Wiederhold 

 * Commit: eb08539e0c9700afa72bb0ebb938eaea810e5d80 (in build: 2275)

   Author: Mike Wiederhold

   MB-23205: Properly handle backups when we are behind the purge seqno

   Change-Id: Iaf1c8d6588d3454e2232a1c23d2a585c0c8d5374

   Reviewed-on: http://review.couchbase.org/74754

   Reviewed-by: Michael Wiederhold 

   Tested-by: Build Bot