Description of problem:
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When setting the global options, 'gluster volume set' provides a way to set them using the volume name as 'all'

But 'gluster volume get' doesn't implement 'all' to get the global options.
So in order to get the global volume options one has to use 'gluster volume get' with specific volume name. This usage makes the illusion as though the option is set only on one volume, which is incorrect.

Retrieving the global volume options ( like op-version, etc ) using the volume name as 'all' should be implemented with 'gluster volume get' functionality


Version-Release number of selected component (if applicable):
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gluster 3.7.9 & mainline 

How reproducible:
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N/A as this is a Feature Request for 'gluster volume get' functionality

Steps to Reproduce:
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N/A as this is a Feature Request for 'gluster volume get' functionality

Actual results:
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With current implementation, the global options are retrieved with 'gluster volume get' functionality using the specific volume name

Expected results:
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'gluster volume get' to implement the way to get the global options using - "gluster volume get all"