Bring semantic versioning to provide for rolling upgrades (#5495)

This PR brings semver capabilities in our RPC layer to
ensure that we can upgrade the servers in rolling fashion
while keeping I/O in progress. This is only a framework change
the functionality remains the same as such and we do not
have any special API changes for now. But in future when
we bring in API changes we will be able to upgrade servers
without a downtime.

Additional change in this PR is to not abort when serverVersions
mismatch in a distributed cluster, instead wait for the quorum
treat the situation as if the server is down. This allows
for administrator to properly upgrade all the servers in the cluster.

Fixes #5393

cmd/storage-rpc-client_test.go

@@ -190,8 +190,8 @@ func TestStorageErr(t *testing.T) {
 			err:         fmt.Errorf("%s", errAuthentication.Error()),
 		},
 		{
-			expectedErr: errServerVersionMismatch,
-			err:         fmt.Errorf("%s", errServerVersionMismatch.Error()),
+			expectedErr: errRPCAPIVersionUnsupported,
+			err:         fmt.Errorf("%s", errRPCAPIVersionUnsupported.Error()),
 		},
 		{
 			expectedErr: errServerTimeMismatch,