Postinstall can no longer be run twice (Traffic Vault load_schema error)

[davidc0le]

This Bug Report affects these Traffic Control components:

• Traffic Ops

Current behavior:

This issue is similar to #4984 . When running postinstall twice when using the Postgres backend for Traffic Vault, the load_schema operation for Traffic Vault causes an error. The command db/admin --trafficvault -env=production load_schema is executed by the postinstall. The error is as follows:

ALTER TABLE ONLY dnssec
    ADD CONSTRAINT dnssec_pkey PRIMARY KEY (cdn);
ERROR:  multiple primary keys for table "dnssec" are not allowed
Can't create database tables

Expected behavior:

As per #4984, running postinstall twice should be possible without errors.

Steps to reproduce:

Run Postinstall with postgres being used for the Traffic Vault backend.
Run Postinstall again with the same input