spacemanager: Allow unreserved transfers even when space reservation for non-srm transfers is enabled

Space manager can be configured to create space reservations for non-srm
transfers. The problem is that as soon as this feature is enabled, all
authenticated non-srm transfers that support space manager must go to a link
group. It isn't possible to mix reserved and unreserved transfers.

This patch addresses this problem by letting space manager fall back to an
unreserved transfer. This fallback already exists if the transfer is
unauthenticated or when a protocol without space- manager support is used.

The patch thus changes the semantics of the property
spacemanager.enable.reserve-space-for-non-srm-transfers. Whereas before
enabling this property would cause some transfers that succeeded before to
fail, the property now only adds additional ways in which a transfer can
succeed. This is easily demonstrated using the system-test package.

Without this patch and with reserve-space-for-non-srm-transfers disabled,
uploading to the reserved directory with gridftp would fail (e.g. 'test
--gridftp -d reserved'), while upload to the disk directory would succeed (e.g.
'test --gridftp -d disk'). If reserve-space-for-non-srm-transfers is enabled,
the success status of these two transfers would be reversed (the former would
now succeed, the latter would now fail). With this patch, enabling
reserve-space-for-non-srm-transfers will cause both uploads to succeed. The
patch thus also changes the default system-test setup to enabel space
reservation for non-srm transfers.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Dmitry Litvintsev <litvinse@fnal.gov>
Patch: http://rb.dcache.org/r/6356