After 8d8f071648d64f8a16591481064e13f590629caa LU-3561 tests: improve sanity-hsm.sh to support remote agent, sanity-hsm.sh can not longer be run out of the box. The newly introduced variables

- AGTCOUNT: number of agents
- AGTDEV{N}: target HSM mount point (root path of the backend)
- agt{N}_HOST: hostname of the agent agt{N}
- SINGLEAGT: facet of the single agent

should be given reasonable fallback values so that sanity-hsm.sh can be run with minimal configuration.