test: do not fail if scsi_debug module not available

On Debian it's only built on amd64 kernels, so skip test cases if it
cannot be loaded

test/units/TEST-17-UDEV.sanity-check.sh

@@ -190,8 +190,8 @@ udevadm test-builtin "factory_reset status" "$loopdev"
 # systemd-hwdb update is extremely slow when combined with sanitizers and run
 # in a VM without acceleration, so let's just skip the one particular test
 # if we detect this combination
-if ! [[ -v ASAN_OPTIONS && "$(systemd-detect-virt -v)" == "qemu" ]]; then
-    modprobe scsi_debug
+# scsi_debug is not available in all architectures/kernels combinations
+if ! [[ -v ASAN_OPTIONS && "$(systemd-detect-virt -v)" == "qemu" ]] && modprobe scsi_debug; then
     scsidev=$(readlink -f /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/[0-9]*)
     mkdir -p /etc/udev/hwdb.d
     cat >/etc/udev/hwdb.d/99-test.hwdb <<EOF

test/units/TEST-35-LOGIN.sh

@@ -298,7 +298,7 @@ teardown_session() (
 
     rm -f /run/udev/rules.d/70-logindtest-scsi_debug-user.rules
     udevadm control --reload
-    rmmod scsi_debug
+    rmmod scsi_debug || true
 
     return 0
 )
@@ -446,7 +446,11 @@ EOF
 
     # coldplug: logind started with existing device
     systemctl stop systemd-logind.service
-    modprobe scsi_debug
+    if ! modprobe scsi_debug; then
+        echo "scsi_debug module not available, skipping test ${FUNCNAME[0]}."
+        systemctl start systemd-logind.service
+        return
+    fi
     timeout 30 bash -c 'until ls /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*:*/block 2>/dev/null; do sleep 1; done'
     dev=/dev/$(ls /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*:*/block 2>/dev/null)
     if [[ ! -b "$dev" ]]; then