Describe the problem
When using the new "Automatic appending incremental backup" UX, backing up full cluster, in two different scenarios, run into the error ERROR: invalid previous backups (a new full backup may be required if a table has been created, dropped or truncated): no backup covers time [1586054134.368267700,0,1586054324.310442218,0) for range [/Table/2/1,/Table/2/2) (or backups out of order) which is weird because that's not a table that's backed up by full cluster restore

To Reproduce
Two scenarios, both running on the same roachprod cluster in AWS on the latest edge binary as of April4 8pmMT

1. Ran ./cockroach workload init tpcc --warehouses=1000 --db=tpcc
2. Took 1 full and 2 incremental backups before init finished, waiting for init to finish
3. Tried to take another backup after init finished and ran into the error (init finishes with a bunch of additions of foreign keys)

Second scenario, same cluster, after init has finished

1. take full backup
2. run tpcc workload ./cockroach workload run tpcc --duration=10m
3. take 2 incremental backups
4. create database (temp)
5. create table (temp.a)
6. drop table (temp.a)
7. attempt another incremental backup--fails
8. workload finishes running