test: don't send image building output to /dev/null (#8886)

Yes, the output is sometimes annyoing, but /dev/null is not the right
place...

I figure this redirection was left in from some debugging session, let's
fix it, and make the setup_basic_environment invocation like in all
other test scripts.

test/TEST-15-DROPIN/test.sh

@@ -9,7 +9,7 @@ TEST_NO_QEMU=1
 
 test_setup() {
         # create the basic filesystem layout
-        setup_basic_environment >/dev/null
+        setup_basic_environment
 
         # mask some services that we do not want to run in these tests
         ln -s /dev/null $initdir/etc/systemd/system/systemd-hwdb-update.service

test/TEST-22-TMPFILES/test.sh

@@ -9,7 +9,7 @@ TEST_NO_QEMU=1
 
 test_setup() {
     # create the basic filesystem layout
-    setup_basic_environment >/dev/null
+    setup_basic_environment
     inst_binary mv
     inst_binary stat
     inst_binary seq