Use a common solana user on all testnet instances

net/scripts/disable-background-upgrades.sh

@@ -1,5 +1,5 @@
 #!/bin/bash -ex
-
+#
 # Prevent background upgrades that block |apt-get|
 #
 # TODO: This approach is pretty uncompromising.  An alternative solution that
@@ -18,4 +18,3 @@ while fuser /var/lib/dpkg/lock; do
   sleep 1
 done
 
-