tests: add test for adding invalid cores devices to caches

Signed-off-by: Damian Raczkowski <damian.raczkowski@intel.com>

test/functional/api/cas/cli_messages.py

@@ -20,6 +20,16 @@ start_cache_with_existing_metadata = [
     r" discard on-disk metadata and start fresh cache instance\."
 ]
 
+start_cache_on_already_used_dev = [
+    r"Error inserting cache \d+",
+    r"Cache device \'\/dev\/\S+\' is already used as cache\."
+]
+
+start_cache_with_existing_id = [
+    r"Error inserting cache \d+",
+    r"Cache ID already exists"
+]
+
 standby_init_with_existing_filesystem = [
     r"A filesystem exists on \S+. Specify the --force option if you wish to add the cache anyway.",
     r"Note: this may result in loss of data"