tests/avocado: Introduce file_truncate()

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20230120134314.81956-2-philmd@linaro.org
[ clg: remove image_pow2ceil_expand() factoring ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>

tests/avocado/boot_linux_console.py

@@ -30,6 +30,11 @@ Round up to next power of 2
 def pow2ceil(x):
     return 1 if x == 0 else 2**(x - 1).bit_length()
 
+def file_truncate(path, size):
+    if size != os.path.getsize(path):
+        with open(path, 'ab+') as fd:
+            fd.truncate(size)
+
 """
 Expand file size to next power of 2
 """