Minor refactoring in the ONOS cell configuration:
 * Each cell-specific variable is explicitly listed
   in the cell config file:
   ONOS_CELL, ONOS_NIC, OC1-OC9, OCN, OCI, ONOS_FEATURES

 * Cleanup and bug fixes inside bash_profile:
   - Don't export explicitly OCI and ONOS_CELL, because those
     are now exported in the cell config file
   - unset ONOS_CELL, ONOS_NIC, ONOS_FEATURES (the last two weren't
     unset before)
   - The built-in "cell" function shows OC1 to OC9 instead of OC0-OC9;
     OC0 is never used/setup anywhere else

 * Added two new shell commands:
   - tools/test/bin/onos-lsit-cells : lists existing ONOS cell configurations
     It is the equivalent of the "cells" built-in bash command
   - tools/test/bin/onos-show-cell : shows the configuration of an ONOS cell
     It is the equivalent of the "cell" built-in bash command, but
     it can show also the configuration of any ONOS cell (not only
     the default one).
diff --git a/tools/test/cells/single b/tools/test/cells/single
index 6dcd4d5..7c03ef4 100644
--- a/tools/test/cells/single
+++ b/tools/test/cells/single
@@ -1,5 +1,10 @@
 # Local VirtualBox-based single ONOS instance & ONOS mininet box
 
+export ONOS_CELL="single"
+
 export ONOS_NIC=192.168.56.*
 export OC1="192.168.56.101"
 export OCN="192.168.56.103"
+export OCI="${OC1}"
+
+export ONOS_FEATURES=""