restapi: Prefering <usages> over <display>

There are two ways setting an network as display
1. The old (dprecated) way- <display>false</display>
2. Thr new way- <usages>
     <usage>display</usage>
   </usages>

If both of them are used the display should be set according to the new
way.

Bug-Url: https://bugzilla.redhat.com/1081005
Change-Id: Ia9794bba6de9803b12a99f146c80d03c82dc4503
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>