Call "replace_all_ziplistvariables_in_rtffile" with a hashref rather
than arrayref.

Also rewrite implementation of installer::scpzipfiles variable
replacement functions, and add test case.  Note that unknown
variables should be ignored rather than replaced with an empty string.

Change-Id: Ic4548b9df8c50cbf2d3049052c637e859542a1e8