Avoid overwrite of the error message in AbortFn

The AbortFn() used to overwrite the error message, hiding the real
failure reported in ErrorAbort(). And we will miss the failure in
the script patterns like 'blockimageupdate() || abort()'

We will ensure there's one line break at the end of ErrorAbort's
error message; and append to the existing error message when calling
abort().

Test: Message from ErrorAbort shows up in the log
Change-Id: I3aebd06629c5129330250c7fe5e8cdead2ae85bc
diff --git a/edify/expr.cpp b/edify/expr.cpp
index 1b8623f..6823b73 100644
--- a/edify/expr.cpp
+++ b/edify/expr.cpp
@@ -114,9 +114,9 @@
 Value* AbortFn(const char* name, State* state, const std::vector<std::unique_ptr<Expr>>& argv) {
     std::string msg;
     if (!argv.empty() && Evaluate(state, argv[0], &msg)) {
-        state->errmsg = msg;
+      state->errmsg += msg;
     } else {
-        state->errmsg = "called abort()";
+      state->errmsg += "called abort()";
     }
     return nullptr;
 }
@@ -410,12 +410,15 @@
 }
 
 Value* ErrorAbort(State* state, CauseCode cause_code, const char* format, ...) {
-    va_list ap;
-    va_start(ap, format);
-    android::base::StringAppendV(&state->errmsg, format, ap);
-    va_end(ap);
-    state->cause_code = cause_code;
-    return nullptr;
+  std::string err_message;
+  va_list ap;
+  va_start(ap, format);
+  android::base::StringAppendV(&err_message, format, ap);
+  va_end(ap);
+  // Ensure that there's exactly one line break at the end of the error message.
+  state->errmsg = android::base::Trim(err_message) + "\n";
+  state->cause_code = cause_code;
+  return nullptr;
 }
 
 State::State(const std::string& script, void* cookie)