chasquid-util: Fix creating the directory on user-add

`chasquid-util user-add` is meant to create the domain directory if it
doesn't exist; however there's a bug that makes this not happen, and
instead the command fails with:

  Error writing database: open <path>: no such file or directory

This patch fixes the issue and adds a test to ensure we don't have any
regressions on this behaviour.

Thanks to raspbeguy (https://github.com/raspbeguy) for reporting this
issue (on IRC).

cmd/chasquid-util/test.sh

@@ -25,13 +25,15 @@ function check_userdb() {
 
 
 rm -rf .config/
-mkdir -p .config/domains/domain/ .data/domaininfo
+mkdir -p .config/ .data/domaininfo
 echo 'data_dir: ".data"' >> .config/chasquid.conf
 
 if ! r print-config > /dev/null; then
 	fail print-config
 fi
 
+# We intentionally run this when the domain directory doesn't exist, as we
+# want to confirm it creates it.
 if ! r user-add interactive@domain --password=passwd > /dev/null; then
 	fail user-add
 fi