Adapt code to new uefi certificates API

See: xapi-project/xen-api#4659

`Host` API is deprecated in favor of `Pool` API

Signed-off-by: BenjiReis <benjamin.reis@vates.fr>

scripts/secureboot-certs

@@ -282,11 +282,6 @@ def session_init():
 
 
 def clear(session):
-    hosts = Host.get_all(session)
-    for host in hosts:
-        host.set_certs(b"")
-        print("Cleared certificates from XAPI DB for host %s." % host.uuid)
-
     for pool in Pool.get_all(session):
         pool.set_certs(b"")
         print("Cleared certificates from XAPI DB for pool %s." % pool.uuid)
@@ -393,10 +388,6 @@ def install(session, args):
     data = base64.b64encode(tarball.getvalue())
     tarball.close()
 
-    hosts = Host.get_all(session)
-    for host in hosts:
-        host.set_certs(data)
-
     pool = Pool.get_all(session)[0]
     if not pool:
         print("Could not retrieve pool from XAPI")
@@ -557,16 +548,9 @@ class Host(object):
     def uuid(self):
         return self.xapi_class.get_uuid(self.opaque_ref)
 
-    def get_certs(self):
-        if self.__certs is None:
-            self.__certs = self.xapi_class.get_uefi_certificates(self.opaque_ref)
-        return self.__certs
-
-    def set_certs(self, data):
-        self.xapi_class.set_uefi_certificates(self.opaque_ref, data)
-
     def save_certs_to_disk(self):
-        decoded = base64.b64decode(self.get_certs())
+        pool = Pool.get_all(self.session)[0]
+        decoded = base64.b64decode(pool.get_certs())
 
         d = cd_tempdir()
         _, fname = tempfile.mkstemp()
@@ -649,6 +633,16 @@ def print_cert(path, uuid, klass, verbose=False):
         print("")
 
 
+def get_certs(self):
+    if self.__certs is None:
+        self.__certs = self.xapi_class.get_uefi_certificates(self.opaque_ref)
+    return self.__certs
+
+
+def set_certs(self, data):
+    self.xapi_class.set_uefi_certificates(self.opaque_ref, data)
+
+
 def report(session, verbose=False):
     try:
         print("\n{} -- Report".format(os.path.basename(sys.argv[0])))