restapi : GET: /api/vms/xxx/reporteddevices returns yaml not xml(#915036)

Api returns yaml for /api/vms/xxx/reporteddevices and
/api/hosts/xxx/hooks

This patch fixes the return type for reporteddevices and
hooks.

Change-Id: I90ff2099da3afd0713bf4a1e48c348c313c4e1ff
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=915036
Signed-off-by: Ravi Nori <rnori@redhat.com>