support any stem for ioc.yaml file

[gilesknap]

This implements the requirement in https://github.com/epics-containers/ibek/issues/82

Completing the issue still requires:

• updating ec to handle any stem for ioc.yaml
• updating the tutorials to encourage unique naming of the ioc yaml
• making sure that liveness.sh is pickiing up the same stem name (somehow - this uses helm chart name at present)