Improve error message when pool was not destroyed/created

This is idempotency related; if a pool does not exist, stratisd will
return success if the user requests that it be destroyed. The CLI wants
to return an error, so it detects lack of change. This change makes the
error message a bit more clear.

Signed-off-by: mulhern <[email protected]>

Author: mulkieran

src/stratis_cli/_actions/_pool.py

@@ -249,7 +249,8 @@ def create_pool(namespace: Namespace):  # pylint: disable=too-many-locals
             raise StratisCliIncoherenceError(
                 (
                     f"Expected to create the specified pool {pool_name} but stratisd "
-                    f"reports that it did not actually create the pool"
+                    "reports that it did not actually create the pool because "
+                    f"a pool with name {pool_name} already exists"
                 )
             )
 
@@ -478,9 +479,10 @@ def destroy_pool(namespace: Namespace):
         if not changed:  # pragma: no cover
             raise StratisCliIncoherenceError(
                 (
-                    f"Expected to destroy the specified pool {namespace.pool_name} but "
-                    f"stratisd reports that it did not actually "
-                    f"destroy the pool requested"
+                    "Expected to destroy the specified pool "
+                    f"{namespace.pool_name} but stratisd reports that it did "
+                    "not actually destroy the pool because no pool named "
+                    f"{namespace.pool_name} was found."
                 )
             )