Give a better name to STOP_REASON_ERROR

It indicates crosvm failed to start the VM, so
STOP_REASON_START_FAILED.

Slightly gratuitously I also renamed the internal DeathReason - mainly
because this is just a much clearer name.

I didn't change the statslog version, because that would just be too
complicated.

Bug: 261037705
Test: atest MicrodroidTests
Change-Id: I5effdba86ea49ff919d82810926fb14ccbbd8499
diff --git a/vmclient/src/death_reason.rs b/vmclient/src/death_reason.rs
index fbf2523..34d89fc 100644
--- a/vmclient/src/death_reason.rs
+++ b/vmclient/src/death_reason.rs
@@ -30,7 +30,7 @@
     /// The VM requested to shut down.
     Shutdown,
     /// crosvm had an error starting the VM.
-    Error,
+    StartFailed,
     /// The VM requested to reboot, possibly as the result of a kernel panic.
     Reboot,
     /// The VM or crosvm crashed.
@@ -66,7 +66,7 @@
             AidlDeathReason::KILLED => Self::Killed,
             AidlDeathReason::UNKNOWN => Self::Unknown,
             AidlDeathReason::SHUTDOWN => Self::Shutdown,
-            AidlDeathReason::ERROR => Self::Error,
+            AidlDeathReason::START_FAILED => Self::StartFailed,
             AidlDeathReason::REBOOT => Self::Reboot,
             AidlDeathReason::CRASH => Self::Crash,
             AidlDeathReason::PVM_FIRMWARE_PUBLIC_KEY_MISMATCH => Self::PvmFirmwarePublicKeyMismatch,