Reexec devstack-vm-gate-wrap as early as possible.

* devstack-vm-gate-wrap.sh: Perform reexec step to test changes to
devstack-gate as early as possible. This is basically after the
workspace is configured.

Change-Id: I6f46b2feddb684efaf1fbf33a766c941eef8e0a7
Merge "Reexec devstack-vm-gate-wrap as early as possible."