util: Resize VM root partition max size to ~128GB

Prior to this change we were limited to a root partition with only 60GB
of space which caused issues when running larger simulations (see:
https://github.com/gem5/gem5/issues/165).

There are two factors in this issue which this patch resolves:

1. The root partition in the VM was capped at 60GB despite the virtual
machines size being capped at 128GB. This resulted in libvirt giving the
VM free space it couldn't use. To fix this `lvextend` was added to the
"provision_root.sh" script to resize the root partition to fill the
available space.
2. The virtual machine size can be set via the `machine_virtual_size`
parameter. The minimum and default value is 128GB. This wasn't exposed
previously. Now, if we required, we can increase the size of the VM/Root
partition if we require (though I believe 128GB is more than sufficient
for now).

Fixes: https://github.com/gem5/gem5/issues/165
Change-Id: I82dd500d8807ee0164f92d91515729d5fbd598e3

util/github-runners-vagrant/Vagrantfile

@@ -40,9 +40,10 @@ Vagrant.configure("2") do |config|
   config.ssh.password = "vagrant"
 
   config.vm.provider "libvirt" do |vb|
-    # Customize the amount of cpus and memory on the VM:
+    # Customize the amount of cpus, memory, and storage on the VM:
     vb.cpus = "4".to_i
     vb.memory = "16384".to_i
+    vb.machine_virtual_size = 128 # 128G is the minimum.
   end
 
   # sets up vm

util/github-runners-vagrant/provision_root.sh

@@ -72,3 +72,6 @@ usermod -aG docker vagrant
 
 # Cleanup
 apt-get autoremove -y
+
+# Resize the root partition to fill up all the free size on the disk
+lvextend -l +100%FREE $(df / --output=source | sed 1d)