Reduce am resource

[mzmssg]

1. reduce AM memory to 1G
2. given Launcher AM might consume 3G+ virtual memory, increase YARN virtual memory ratio to 6, previous value is 2.1.

Test case:
A framework with 9 taskroles, 5 tasks per taskrole, 2-node cluster, for one hour.

[coveralls]

Coverage increased (+0.2%) to 52.845% when pulling 97b76fd on zimiao/reduce_am_resource into f0fe0d9 on master.

[coveralls]

Coverage remained the same at 52.68% when pulling 5d43fab on zimiao/reduce_am_resource into f0fe0d9 on master.

[Gerhut]

Shall we make it as default config in launcher?

[yqwang-ms]

By setting this, it is already default for all jobs.

[mzmssg]

@Gerhut
Seems it would be better of putting it in job config instead hard-code here?

[mzmssg]

@Gerhut
Updated