Convert case only for seleted neutron methods

Instead of converting cases in all requsts, just do so in the
Neutron requests.

Change-Id: I17beba58514e28a566a3e847ebd900d24deb07b5
Fixes: MN-2761
Signed-off-by: Ryu Ishimoto <ryu@midokura.com>
Merge "Convert case only for seleted neutron methods"