Review Request 65351: Reordered roles in Web UI to display them alphabetically by default.

[Armand Grillet]

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Review request for mesos and Benjamin Mahler.


Bugs: MESOS-8495
    https://issues.apache.org/jira/browse/MESOS-8495


Repository: mesos


Description
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Use the alphabetical order of the name of the roles by
default to display their hierarchy straightforwardly.


Diffs
-----

  src/webui/master/static/js/app.js 463c563cd121e881f7d137123534a047c5e420d2 
  src/webui/master/static/roles.html 7578852e4e2ad29a0f07e16dcff85af6a2255b02 


Diff: https://reviews.apache.org/r/65351/diff/1/


Testing
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```
$ bash mesos-master.sh --port='5061' --work_dir='/tmp/master1' 
--webui_dir='/Users/Armand/Code/apache-mesos/src/webui' 
--log_dir='/tmp/master1-log' --weights="example=42,example/a=2" 
--registry=in_memory
```
UI before patch when viewing the roles tab:
![Old UI](https://i.imgur.com/dflxj11.png)
UI by default after patch:
![New UI](https://i.imgur.com/PRyAwNs.png)


Thanks,

Armand Grillet