Reflectometry: Start Seci should not wait for SECI to exit (currently does)

[John-Holt-Tessella]

As a developer and user I don't want the stop_ibex_server_start_seci to wait for SECI to complete before exiting.

Acceptance Criteria

• Script completes after starting seci

[John-Holt-Tessella]

pull requests

• https://github.com/ISISComputingGroup/EPICS/pull/223