ICSHWI-9056 Support require-4

The first commit merges start_conda_ioc.sh and start_nfs_ioc.sh into a unified start_ioc.sh (and changes the realtime check a bit because the unification changed the filename of the generated st.cmd).

The second commit adds support for require-4; instead of checking the version specified in ioc.yml it just checks if iocsh exists. env.sh is loaded only for require-3.