Fix LDAP updates in ipa-replica-install

ipalib API needs to be bootstrapped in 'installer' context otherwise
LDAP update plugins don't get initialized and ipa-replica-install
crashes.

https://fedorahosted.org/freeipa/ticket/2139

install/tools/ipa-replica-install

@@ -354,7 +354,7 @@ def main():
     finally:
         os.umask(old_umask)
 
-    api.bootstrap(in_server=True)
+    api.bootstrap(in_server=True, context='installer')
     api.finalize()
 
     # Create DS group if it doesn't exist yet