boot/zephyr: Added single-slot Zephyr-RTOS test build

Added configuration for build in Zephyr-RTOS CI MCUBoot
in CONFIG_SINGLE_APPLICATION_SLOT=y mode.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/sample.yaml b/boot/zephyr/sample.yaml
index 6c41d28..048a588 100644
--- a/boot/zephyr/sample.yaml
+++ b/boot/zephyr/sample.yaml
@@ -18,3 +18,8 @@
       DTC_OVERLAY_FILE=./boards/nrf52840_big.overlay
     platform_allow:  nrf52840dk_nrf52840
     tags: bootloader_mcuboot
+  sample.bootloader.mcuboot.single_slot:
+    extra_args: OVERLAY_CONFIG=./single_slot.conf
+      DTC_OVERLAY_FILE=./boards/nrf52840_single_slot.overlay
+    platform_allow:  nrf52840dk_nrf52840
+    tags: bootloader_mcuboot