client: add support for --strict-copy flag
Motivation: There are some circumstances in which it is impossible for FTS to verify that a transfer was successful: any attempt to do so will fail, which results in the overall transfer failing. Rather than failing transfers, it may be acceptable to rely on the result of the COPY. If this reports success then consider the transfer successful. Support for this already exists in FTS. It is only the REST client that is missing a flag. Modification: Add the `strict_copy` param with a default value of `False`. Add a command-line argument that switches on the behaviour. Result: Someone using the REST client is now able to tell FTS that files are to be copied without FTS attempting to verify the success.