updater_sample: update tests

- fix tools/gen_update_config.py
- add tests for PayloadSpecs#forStreaming

Test: junit4
Change-Id: Ife1980c5f72944ed35500aa820b30031fc99e820
Signed-off-by: Zhomart Mukhamejanov <zhomart@google.com>
diff --git a/updater_sample/tools/gen_update_config.py b/updater_sample/tools/gen_update_config.py
index cb9bd01..0578124 100755
--- a/updater_sample/tools/gen_update_config.py
+++ b/updater_sample/tools/gen_update_config.py
@@ -17,7 +17,7 @@
 """
 Given a OTA package file, produces update config JSON file.
 
-Example:  tools/gen_update.config.py \\
+Example:  tools/gen_update_config.py \\
             --ab_install_type=STREAMING \\
             ota-build-001.zip  \\
             my-config-001.json \\