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Hi team,

I'm planning to move "common-rst" to "common" at master branch.
I think the name "common" is simple to use.

At now, the "common" directory contains only one XML entity file.
So, it's not confusable to merge contents to the "common" directory.

The operations-guide repo doesn't have the "common" and
"common-rst" directory. This change dones't affect it.

Also, this change doesn't affect translations because
the strings doesn't change, and administrator can copy strings.
Just name change at their translation system "Zanata".

Any thought?

Regards,
KATO Tomoyuki