Update stable to SD-Fabric v1.0 RC1

TODO
- Publish ONOS artifacts for 2.5.5-rc1 - DONE
- Merge PR and tag trellis-control for 3.1.0-rc1 - DONE
    Jenkins refuses to tag non SemVer versions
    https://gerrit.onosproject.org/c/trellis-control/+/25055
- Merge PR and tag trellis-t3 for 4.0.0-rc1 - Done
    Jenkins refuses to tag non SemVer versions
    https://gerrit.onosproject.org/c/trellis-t3/+/25058
- Merge PR and tag fabric-tna for 1.0.0-rc1 - DONE
    https://github.com/stratum/fabric-tna/pull/403
- Merge PR and tag up4 for 1.0.0-rc1 - DONE
    https://github.com/omec-project/up4/pull/186

Also, provide means to skip trellis-t3, which is currently not used in
SD-Fabric.

Change-Id: I4a7ecd2df4f42b59e475382461fcd22d56649bf7
diff --git a/Makefile.vars.master b/Makefile.vars.master
index 8a11652..29ffc95 100644
--- a/Makefile.vars.master
+++ b/Makefile.vars.master
@@ -27,7 +27,7 @@
 # (3) Fetch from Gerrit/Github (pending review in the form of refs/changes/... or pending pull request);
 
 export ONOS_VERSION            ?= onos-2.5
-export TRELLIS_CONTROL_VERSION ?= 3.0.1-SNAPSHOT
+export TRELLIS_CONTROL_VERSION ?= 3.1.0-SNAPSHOT
 export TRELLIS_T3_VERSION      ?= 4.0.0-SNAPSHOT
 export UP4_VERSION             ?= master
 export FABRIC_TNA_VERSION      ?= main
diff --git a/Makefile.vars.stable b/Makefile.vars.stable
index a7d86cd..d733531 100644
--- a/Makefile.vars.stable
+++ b/Makefile.vars.stable
@@ -26,8 +26,8 @@
 # (2) Checkout Local source code (local branch not yet pushed);
 # (3) Fetch from Gerrit/Github (pending review in the form of refs/changes/... or pending pull request);
 
-export ONOS_VERSION            ?= cf5dabd3dd6b1a94fb718da6fe8d5e95ef1e5479
-export TRELLIS_CONTROL_VERSION ?= 02fd3b0d4943c98524f30348026dc986f24dce2d
-export TRELLIS_T3_VERSION      ?= 4fd3b46d76d1738c3d69d5fdc56603ac77fbfdc0
-export UP4_VERSION             ?= 9d42eb45b86f9720d0d45f9dc9cf62804a9921a3
-export FABRIC_TNA_VERSION      ?= e4d9beabba84e1d6f378e6806dceb1d4643a7606
+export ONOS_VERSION            ?= 2.5.5-rc1
+export TRELLIS_CONTROL_VERSION ?= 3.1.0-rc1
+export TRELLIS_T3_VERSION      ?= 4.0.0-rc1
+export UP4_VERSION             ?= 1.0.0-rc1
+export FABRIC_TNA_VERSION      ?= 1.0.0-rc1
diff --git a/README.md b/README.md
index 28d4145..762f296 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,10 @@
 # TOST ONOS Development Build Environment
 
-Docker build environment capable of producing a version of **ONOS** and needed apps that can run with **TOST**. Typically the **ONOS** restful api would be used to include apps after **ONOS** is started.
+Docker build environment capable of producing a version of **ONOS** and needed apps that make the SD-Fabric control plane.
+
+The name TOST comes from the early days of the SD-Fabric project. It stands for Trellis ONOS Stratum Tofino. We keep this name for backward compatibility.
+
+Typically the **ONOS** restful api would be used to include apps after **ONOS** is started.
 
 ## Build