restapi: Ignore case in CPU architecture

The validation of the CPU architecture should be done ignoring case.

Change-Id: Ib06b176dcc48fac667713683bdae5b1cfe4a4332
Bug-Url: https://bugzilla.redhat.com/1129248
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>
(cherry picked from commit 4aaf8105c673820713dd219787a7149fcc59996e)