Create a ZRAM swap device

Implement simple mkswap/swapon functionality within microdroid
manager. Use it to configure a ZRAM swap device.

Bug: 238284600
Test: Start a VM, confirm swap is available
Change-Id: I8757d1f9118c1fc14d4e8c9580e37d60d699d264
diff --git a/microdroid_manager/src/main.rs b/microdroid_manager/src/main.rs
index a6856d0..78f8bb4 100644
--- a/microdroid_manager/src/main.rs
+++ b/microdroid_manager/src/main.rs
@@ -18,6 +18,7 @@
 mod instance;
 mod ioutil;
 mod payload;
+mod swap;
 mod vm_payload_service;
 
 use crate::dice::{DiceContext, DiceDriver};
@@ -170,6 +171,9 @@
 
     load_crashkernel_if_supported().context("Failed to load crashkernel")?;
 
+    swap::init_swap().context("Failed to initialise swap")?;
+    info!("swap enabled.");
+
     let service = get_vms_rpc_binder()
         .context("cannot connect to VirtualMachineService")
         .map_err(|e| MicrodroidError::FailedToConnectToVirtualizationService(e.to_string()))?;