The dynamic inventory script only requires shade when querying
ironic for a list of hardware resources. As we may not have
completed the installation sequence, shade may not be present.
Added a check to attempt to load shade and then error if a user
attempts to use the script to query ironic with shade missing.
Change-Id: I300e043bd76d4872781b42e05a5eb76a30a74f5e
95d28e0eee