In legacy/trac#18240, cypherpunks pointed out that we should use the same `$(EXEEXT)` syntax for finding the appropriate `tor-gencert` and `tor-cov-gencert` in the `test-network` target. There's a couple other problems with that target: * `NETWORK_FLAVOUR=${NETWORK_FLAVOUR:-"bridges+hs"}`: the "bridges+hs" network template doesn't exist anymore. * If `$use_coverage_binary` is set when `src/test/test-network.sh` is called, then chutney will still try to use `tor-gencert` instead of `tor-cov-gencert`. (Also the filename extension problem mentioned above applies here also.