Add option for IDS to be tolerant of restore failures

[kevinphippsstfc]

This is an issue experienced by both Diamond and ESRF where in both cases it is known that there are entries in ICAT which do not have corresponding files available on the tape archive system. Currently the IDS is very strict and will not allow a retrieval to continue if it finds that there are any files that are not available from the archive storage.

For both Diamond and ESRF the IDS is only used in read only mode (only for restores - no deleting or writing) so it is safer to ignore the restore failures than for an IDS that also does write operations.

What is envisaged is an optional property in the run.properties file that if set to true, causes the IDS to be more tolerant of failures and only to fail if all of the items requested by the user are unavailable. The default behaviour would be for the IDS to continue to behave as it does currently.

In cases where there are failures, a list of the failures will be written to a file that is inserted into the downloaded zip file, with the name and location of this file being configurable via another property.