add ability to set quota on gluster volumes

Since the "bricks" of a gluster cluster will just be zfs datasets underneath the hood, we need a way for gluster to be "aware" of zfs based quotas that have been set on those "bricks" that make up the zpool.

This is for accurate calculation of the total gluster volume size during creation.

There is a gluster volume feaure "quota-deem-statfs" which uses the standard "df" utility to determine the size of the "brick". I need to add a "quota" api endpoint so the quota option can be turned on. Once the quota has been turned on, the existing api endpoint (optset) can be used to set "quota-deem-statfs" on the gluster volume.