Update owners aliases for shared groups to match what is currently (#453)

defined in the aws provider and add security contacts (sig leads).

Author: Robert Bailey

OWNERS_ALIASES

@@ -2,27 +2,18 @@
 
 aliases:
   sig-cluster-lifecycle-leads:
-    - lukemarsden
+    - justinsb
     - luxas
-    - roberthbailey
     - timothysc
   cluster-api-admins:
+    - davidewatson
+    - detiber
     - justinsb
-    - krousey
-    - luxas
-    - roberthbailey
-    - kris-nova
   cluster-api-maintainers:
-    - jessicaochen
-    - k4leung4
-    - karan
-    - kris-nova
-    - krousey
-    - medinatiger
-    - mkjelland
-    - roberthbailey
-    - rsdcastro
-    - spew
+    - detiber
+    - justinsb
+    - ncdc
+    - vincepri
   sig-openstack-leads:
     - hogepodge
     - dklyle

SECURITY_CONTACTS

@@ -10,5 +10,6 @@
 # DO NOT REPORT SECURITY VULNERABILITIES DIRECTLY TO THESE NAMES, FOLLOW THE
 # INSTRUCTIONS AT https://kubernetes.io/security/
 
-bob
-alice
+justinsb
+luxas
+timothysc