Fix gppkg's coordinator hook not execute.
old (and current) gppkg create the package like this format:
```
PostInstall:
- Master:  "sh ./master.sh"
- Segment: "sh ./segment.sh';"
- All:     "echo 'install successful'"
```
sed -i s/master/coordinator/g will break this behavior.
@@ -1141,7 +1141,7 @@ class PerformHooks(Operation):
if key is None:
return
key_str = key[0]
- if key_str.lower() == 'coordinator':
+ if key_str.lower() in ('coordinator', 'master'):
if self.standby_host:
RemoteCommand(hook[key_str], [self.standby_host]).run()
LocalCommand(hook[key_str], True).run()
