Comment 1 for bug 1802219

[1]https://git.launchpad.net/plainbox-provider-snappy/tree/units/usb/usb.pxu

[2] Example of a system that has usb3 bus:
u@localhost:~$ checkbox-snappy.checkbox-cli run com.canonical.certification::removable_partition
===========================[ Running Selected Jobs ]============================
--------------[ Running job 1 / 1. Estimated time left: 0:00:00 ]---------------
----------------[ Collect removable partitions info from udev ]-----------------
ID: com.canonical.certification::removable_partition
Category: com.canonical.plainbox::uncategorised
... 8< -------------------------------------------------------------------------
path: /devices/pci0000:00/0000:00:13.0/0000:01:00.0/rtsx_pci_sdmmc.0/mmc_host/mmc1/mmc1:59b4/block/mmcblk1/mmcblk1p1
name: mmcblk1p1
bus: mmc
category: PARTITION
product: mmcblk1p1
product_slug: mmcblk1p1

path: /devices/pci0000:00/0000:00:15.0/usb2/2-1/2-1:1.0/host2/target2:0:0/2:0:0:0/block/sdb/sdb1
name: sdb1
bus: usb3
category: PARTITION
product: sdb1
product_slug: sdb1