RFE: usecase request (upgrade validation)

[amarts]

Usecase: I need to be able to test upgrade from version a.b.c -> x.y.z

Recently we are hearing usecases from many users who have older versions, and want to seemlessly upgrade to higher version.

Just to make sure we are comfortable with this, we need a test case, which does below steps:

upgrade.t

BUILD v3.8.8 (should pick up the tag and build)
node1 INSTALL v3.8.8

install the specific version code.
... run volume create,  volume start, mount, and some basic I/O. ...

BUILD v7.7
node1 INSTALL v7.7
node4 INSTALL v7.7
...
restart the glusterd process.
restart volumes. (may be a `pkill gluster`, and `gluster volume start`)
check if the client mount still has access to the server.

Now, upgrade the cluster.op-version to a higher value, and see if the client still has access.
...

NOTE: above is a pseudo code, and actual implementations can differ!