nixos/tests/prometheus-2.nix: increase diskSize of the store machine

This is to fix the following error in the test on aarch64-linux:

store# [  126.911144] thanos[739]: level=error ts=2019-06-16T14:00:26.59870538Z caller=main.go:182 msg="running command failed" err="error executing compaction: first pass of downsampling failed: create dir: mkdir /var/lib/thanos-compact/downsample: no space left on device"
store# [  126.942655] systemd[1]: thanos-compact.service: Main process exited, code=exited, status=1/FAILURE

1 files changed, 1 insertions, 0 deletions

diff --git a/nixos/tests/prometheus-2.nix b/nixos/tests/prometheus-2.nix
index 3e2c675b7c62..219c47c73d95 100644
--- a/nixos/tests/prometheus-2.nix
+++ b/nixos/tests/prometheus-2.nix
@@ -132,6 +132,7 @@ in import ./make-test.nix {
     };
 
     store = { pkgs, ... }: {
+      virtualisation.diskSize = 2 * 1024;
       environment.systemPackages = with pkgs; [ jq thanos ];
       services.thanos.store = {
         enable = true;