This patch is replacing the ironic-inspector own implementation for
validating the root device hints in favor of the standard one from
ironic-lib.
The implementation in ironic-lib is flexible enough and fits in
ironic-inspector well so no big updates to functional or unittests
are needed.
A new dependency for ironic-lib was added to requirements.txt.
Change-Id: I0f2b8f463232d0d5b42d0b6e343d5c6e336d32c7
Closes-Bug: #1648133
891639612b