ItemUpdater: Validate BMC squashfs image

- Validate the image dir by checking its content.
- Set Activation to "Active" if current image,
  "Ready" if validation passed and "Invalid" if
  validation fails

Resolves openbmc/openbmc#1629

Change-Id: I5f1c42fb2ba93c849ea8653c9e81c737ae27c814
Signed-off-by: Saqib Khan <khansa@us.ibm.com>
2 files changed