Update to improved system_properties API.

Bug: 217728265
Test: mm
Change-Id: I1ba1af10988f8f98318cff72488c4e600853938e
diff --git a/keystore2/src/metrics_store.rs b/keystore2/src/metrics_store.rs
index b18d84c..b6f1343 100644
--- a/keystore2/src/metrics_store.rs
+++ b/keystore2/src/metrics_store.rs
@@ -649,6 +649,7 @@
 pub fn read_keystore_crash_count() -> Result<i32> {
     rustutils::system_properties::read("keystore.crash_count")
         .context("In read_keystore_crash_count: Failed read property.")?
+        .context("In read_keystore_crash_count: Property not set.")?
         .parse::<i32>()
         .map_err(std::convert::Into::into)
 }