After upgrading from 7.3 to 7.4, ipa-server-upgrade script fails with the error: "This entry already exists"

Issue

After upgrading from 7.3 to 7.4 ipa-server-upgrade script fails with the error: "This entry already exists"

We see the following errors in /var/log/ipaupgrade.log

2017-08-07T05:57:36Z ERROR Upgrade failed with This entry already exists
2017-08-07T05:57:36Z DEBUG Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/ipaserver/install/upgradeinstance.py", line 220, in __upgrade
    self.modified = (ld.update(self.files) or self.modified)
  File "/usr/lib/python2.7/site-packages/ipaserver/install/ldapupdate.py", line 911, in update
    self._run_updates(all_updates)
  File "/usr/lib/python2.7/site-packages/ipaserver/install/ldapupdate.py", line 883, in _run_updates
    self._run_update_plugin(update['plugin'])
  File "/usr/lib/python2.7/site-packages/ipaserver/install/ldapupdate.py", line 859, in _run_update_plugin
    restart_ds, updates = self.api.Updater[plugin_name]()
  File "/usr/lib/python2.7/site-packages/ipalib/frontend.py", line 1470, in __call__
    return self.execute(**options)
  File "/usr/lib/python2.7/site-packages/ipaserver/install/plugins/upload_cacrt.py", line 84, in execute
    ldap.update_entry(entry)
  File "/usr/lib/python2.7/site-packages/ipapython/ipaldap.py", line 1553, in update_entry
    self.conn.modify_s(str(entry.dn), modlist)
  File "/usr/lib64/python2.7/contextlib.py", line 35, in __exit__
    self.gen.throw(type, value, traceback)
  File "/usr/lib/python2.7/site-packages/ipapython/ipaldap.py", line 973, in error_handler
    raise errors.DuplicateEntry()
DuplicateEntry: This entry already exists

We also see the following in error logs

[09/Aug/2017:08:47:46.749628463 +0300] conn=5 op=354 ADD dn="cn=UNIX.LOCAL IPA CA,cn=certificates,cn=ipa,cn=etc,dc=unix,dc=local"
[09/Aug/2017:08:47:46.752797302 +0300] conn=5 op=354 RESULT err=19 tag=105 nentries=0 etime=0

[09/Aug/2017:08:47:46.753397923 +0300] conn=5 op=355 MOD dn="cn=UNIX.LOCAL IPA CA,cn=certificates,cn=ipa,cn=etc,dc=unix,dc=local"
[09/Aug/2017:08:47:46.753732945 +0300] conn=5 op=355 RESULT err=19 tag=103 nentries=0 etime=0

LDAP Error code 19 : LDAP_CONSTRAINT_VIOLATION