sw:vec: test_runner: grab elf return code

Grab the return code from the log string. Ideally we would like to grab
the result from CSR or a register, but QEMU doesn't have the register
access hooked up. :(

With this change, test_runner.py will tunnel the main return code, and
can be used in CI or ctest.

Change-Id: I6dfbf9cb1b4f4911bcfb230936c67f255178ee7c

scripts/test_runner.py

diff --git a/scripts/test_runner.py b/scripts/test_runner.py
index f603d40..f9e3c72 100755
--- a/scripts/test_runner.py
+++ b/scripts/test_runner.py
@@ -129,6 +129,12 @@
     failure_strings = ["FAILED", "Exception occurred"]
     if any(x in output for x in failure_strings):
         sys.exit(1)
+    # Grab the return code from the output string with regex
+    # Syntax: "main returned: ", <code> (<hex_code>)
+    return_string = re.compile(
+        r"\"main returned:\s\",(?P<ret_code>\s[0-9]+\s*)")
+    code = return_string.search(output)
+    sys.exit(int(code.group(1)))
 
 
 if __name__ == "__main__":