* spec/fabricators/fabricator.rb (random_mac, random_asset): downcase result

We normalize these pieces of data in Razor::Data::Node.canonicalize_hw_info
so that they are always lower case in the database. This makes sure that
fabricated objects adhere to that.
Rudimentary search of nodes by hostname and hw_info

It is now possible to search the nodes collection by these criteria; the
value of the hostname parameter can be a regular expression, the hw_info
attributes are searched with an exact match.

Some examples:

  /api/collections/nodes?hostname=host.*
      find hosts whose name starts with 'host'

  /api/collections/nodes?mac=00:de:ad:be:ef:00
                        ?asset=ABCDE
                        ?uuid=UUUU...UUUU
      find a node whose mac/asset tag/uuid is exactly the given value
Add a modify-policy-max-count command to change a policy's max-count
Add nodes and policies subcollections to tags

This makes it possible to find all nodes tagged with a certain tag, and all
policies in which a tag is used
Add a nodes subcollection to policies

This makes it possible to find all nodes that use a certain policy