Upgrade from 4.2.4 to 5.1 fails with ORA-00955: name is already used by an existing object

Steps to reproduce

1. Setup 4.2.4 against Oracle
2. Export the 4.2.4 DB SQL Developer [ Tools => Database export ]
3. Setup 5.1.1 instance
4. Drop/recreate the existing alfresco tablespace
5. Execute the .sql file generated by the export
6. Start 5.1 instace

Actual result

2017-01-10 16:03:34,860 ERROR [org.alfresco.repo.domain.schema.SchemaBootstrap] [localhost-startStop-1] Schema auto-update failed
java.sql.SQLSyntaxErrorException: ORA-00955: name is already used by an existing object

	at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:445)
	at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:396)

Expected result
No error

Notes

• Customer reproduced this using Oracle's expdp/impdp
• Reproducible inhouse using SQL Developer tool
• This is not reproducible using the classic oracle's exp/imp utilities.
• The workaround for this is to drop the index as per article 000008859 but logging it as jira so the upgrade script deletes the existing index before trying to create it.

  alter table ACT_RE_PROCDEF drop constraint ACT_UNIQ_PROCDEF;
  drop index ACT_UNIQ_PROCDEF;
  alter table ACT_RE_PROCDEF add constraint ACT_UNIQ_PROCDEF unique (KEY_,VERSION_);