Ignore row on duplicate key in filemetadata

Currently we are getting a lot of errors:
`[21/Jul/2014:02:02:31]    IntegrityError: ORA-00001: unique constraint (CMS_ANALYSIS_REQMGR.PK_TASKLFN) violated` 
With this `IGNORE_ROW_ON_DUPKEY_INDEX(filemetadata, PK_TASKLFN)` if primary key already matches no rows will be inserted and no more big number of errors in the log files.

```
From 20140714 to 20140721
grep 'IntegrityError: ORA-00001: unique constraint (CMS_ANALYSIS_REQMGR.PK_TASKLFN) violated' vocms136/crabserver/crabserver-201407*.log | wc -l
6381
```