Add group-node-maps to return node maps

Returns a sequence of node maps for the specified group specs.
Fix ensure-service-dispatch in hybrid provider
Add spool-root to p.script.lib

Returns the root directory for spool files, usually /var/spool.
Log ssh port when executing remote scripts
Allow tmpdir specification in make-temp-file
Allow action specific script context

The :script-context action option can be used to specify a sequence of additional
script context keywords for an action.
Allow control of hashing in scripts

The :script-hash option can be used to control whether the shell hashes executable
paths.  Defaults to true.
Ensure ssh-mktemp respects TMPDIR in :script-env