(#6112) Fix memory indirector search in ca specs

The Memory indirector search tries to look up keys including the given
search key, but the SslFile indirectors which we are bypassing simply
return all files from the directory on a search.  This patch applies a
dummy search to the memory indirectors so that all in memory instances
are returned, simulating the directory contents lookup.  Without this it
turns out that we aren't testing autosigning because no csrs are found
to autosign.