Fixes nits, modifies unit tests.
This is a follow-up to commit c5544fb7a0d9d2a1481b3256c3587259368b599e.
Change-Id: Ibca82cc6e32311b1ff0be7137d8392f63e12639b
Closes-Bug: #1635057
Implements an optional collector 'collect_dmidecode_info' for
collecting detailed info of processor, memory and BIOS and
adds it to the inspection data.
Collects BIOS, processor, memory info and adds under the 'dmi' key.
Change-Id: Ida9b418ca579b15de70d17886631f3b21697987e
Closes-Bug: #1635057