cmake: set IS_TEST in the samples that were including Makefile.test

For an unknown reason, various samples in KBuild were including
Makefile.test, this had some desired benefits, one of which is that
the popular BOOT_BANNER appears. The CMake-equivalent of including
Makefile.test is setting the flag IS_TEST. This commit reverts the
behaviour of the samples back to how it was pre-cmake.

Signed-off-by: Sebastian Boe <sebastian.boe@nordicsemi.no>
diff --git a/samples/bluetooth/mesh_demo/CMakeLists.txt b/samples/bluetooth/mesh_demo/CMakeLists.txt
index adc8d0f..2a023b3 100644
--- a/samples/bluetooth/mesh_demo/CMakeLists.txt
+++ b/samples/bluetooth/mesh_demo/CMakeLists.txt
@@ -1,4 +1,5 @@
 set(QEMU_EXTRA_FLAGS -s)
+set(IS_TEST 1)
 
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
diff --git a/samples/boards/microbit/display/CMakeLists.txt b/samples/boards/microbit/display/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/boards/microbit/display/CMakeLists.txt
+++ b/samples/boards/microbit/display/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/boards/microbit/pong/CMakeLists.txt b/samples/boards/microbit/pong/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/boards/microbit/pong/CMakeLists.txt
+++ b/samples/boards/microbit/pong/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/boards/microbit/sound/CMakeLists.txt b/samples/boards/microbit/sound/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/boards/microbit/sound/CMakeLists.txt
+++ b/samples/boards/microbit/sound/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/mpu/mem_domain_apis_test/CMakeLists.txt b/samples/mpu/mem_domain_apis_test/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/mpu/mem_domain_apis_test/CMakeLists.txt
+++ b/samples/mpu/mem_domain_apis_test/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/mpu/mpu_stack_guard_test/CMakeLists.txt b/samples/mpu/mpu_stack_guard_test/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/mpu/mpu_stack_guard_test/CMakeLists.txt
+++ b/samples/mpu/mpu_stack_guard_test/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/mpu/mpu_test/CMakeLists.txt b/samples/mpu/mpu_test/CMakeLists.txt
index 92a4288..931171f 100644
--- a/samples/mpu/mpu_test/CMakeLists.txt
+++ b/samples/mpu/mpu_test/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)
 
diff --git a/samples/synchronization/CMakeLists.txt b/samples/synchronization/CMakeLists.txt
index 6daa0b7..2a129c2 100644
--- a/samples/synchronization/CMakeLists.txt
+++ b/samples/synchronization/CMakeLists.txt
@@ -1,3 +1,5 @@
+set(IS_TEST 1)
+
 include($ENV{ZEPHYR_BASE}/cmake/app/boilerplate.cmake NO_POLICY_SCOPE)
 project(NONE)