imgtool: Add missing requirements to requirements.txt file

Signed-off-by: Rustam Ismayilov <rustam.ismayilov@arm.com>
Change-Id: I9c84e544b466c0e041bb947fb4dd3e01b0d38ae5
diff --git a/scripts/requirements.txt b/scripts/requirements.txt
index 79883b6..36cbbc5 100644
--- a/scripts/requirements.txt
+++ b/scripts/requirements.txt
@@ -2,4 +2,6 @@
 intelhex
 click
 cbor2
+setuptools
 pyyaml
+pytest