Revise code of gsi_util help

The patch unifies the code of arguments '--vendor' and '--system',
and to be an argument group 'image sources'.

Bug: 64817940
Test: gsi_util.py for each commands and check the output
Change-Id: I591ef4b922f931b7ceaacc362979156ef830a54e
diff --git a/gsi/gsi_util/Android.bp b/gsi/gsi_util/Android.bp
index c1b2828..d1b1131 100644
--- a/gsi/gsi_util/Android.bp
+++ b/gsi/gsi_util/Android.bp
@@ -19,6 +19,7 @@
     "gsi_util/*.py",
     "gsi_util/checkers/*.py",
     "gsi_util/commands/*.py",
+    "gsi_util/commands/common/*.py",
     "gsi_util/dumpers/*.py",
     "gsi_util/mounters/*.py",
     "gsi_util/utils/*.py",