Updated custom commands to run as iwadmin

Since the webmin role can't guarantee the presence of the "admin"
user in the system it is globally safer to run using the "iwadmin"
user that is guaranteed to be present.

Issue: IWSoftware/ekahau-rtls-playbook#1
Ticket: #5507

Signed-off-by: Nathan Callister <ncallister@iwsoftware.com.au>