[fx] update run-host-tests -z to use build.

"fx run-host-tests -z" used the removed command "build-zircon" before
running tests. Update it to use the normal "build" which now builds
zircon too.

Change-Id: Iaaccb01f9155e3989c68c55612cedf0d92ee1224

tools/devshell/run-host-tests

@@ -39,7 +39,7 @@ function main {
 
   if [[ $ZIRCON -eq 1 ]]; then
     host_test_dir="${ZIRCON_BUILDROOT}/host_tests"
-    fx-command-run build-zircon "-v"
+    fx-command-run build "-v"
     runtests_cmd=("${ZIRCON_TOOLS_DIR}/runtests")
 
     if [[ -n "$TEST_NAMES" ]]; then