Bug fixes.

- Fixed a regression with the -p option.

- Fixed the basic.n7 test caused by renaming the N7_NO_SUBPROCESS env
  var.

- Renamed N7::local::files::cp_tpl to N7::local::files::bash_tpl that
  does only templating.

- Documented how to do variable assignments in a bash template.

- Make N7::local::files::cp takes a tplcmd option that specifies the
  templating command to use on the source file. The templating then
  is done for each remote host, passing the N7_HOST env var, allowing
  variable substitutions to be done with respect to each remote host.