test/py: gpt: add test for sub-command read and verify

add sandbox test for some gpt sub-command
- gpt read / part list : read the gpt partition created by sgdisk on host
  test start, size, LBA and name output
- gpt verify : verify the gpt partition create by sgdisk on host

PS: persistent data test_gpt_disk_image.bin are udpated

Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>