Rename /controller/servers to /controller/hypervisors

gns3server/handlers/api/controller/__init__.py

@@ -15,5 +15,5 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from .server_handler import ServerHandler
+from .hypervisor_handler import HypervisorHandler
 from .version_handler import VersionHandler