build_library: Change default MINIOS partition size for some layouts

Change the MINIOS B partition to be smaller for usb or recovery images
since it will be empty.

BUG=b:186242954
TEST=run build images which uses the usb format, unpack partitions to
verify correct USB size for MINIOS-B, then cros flash
and check partition table

Change-Id: Ic0a2cd17ab2e06a75dce19038908550c44b18c12
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2871109
Tested-by: Vyshu Khota <vyshu@google.com>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/build_library/minios_disk_layout.json b/build_library/minios_disk_layout.json
index 112ca87..37b4b09 100644
--- a/build_library/minios_disk_layout.json
+++ b/build_library/minios_disk_layout.json
@@ -25,6 +25,21 @@
         # Places partition at the end of disk.
         "features": ["last_partition"]
       }
+    ],
+    # Used for bootable USB installs (not recovery).
+    "usb": [
+      {
+        # MiniOS Slot B unused on usb.
+        "num": 14,
+        "size": "2 MiB"
+      }
+    ],
+    "recovery": [
+      {
+        # MiniOS Slot B unused on recovery.
+        "num": 14,
+        "size": "2 MiB"
+      }
     ]
   }
 }