Bug 1554043 - Make the valgrind-test error when valgrind exits with a non-zero code slightly more useful. r=dmajor

The exit code from valgrind may subtly indicate how it failed (like, if
it's 139 or 137, which would mean respectively segfault or killed by
something external), which is currently completely hidden, making
diagnostics of things like bug 1545094 harder.

Differential Revision: https://phabricator.services.mozilla.com/D32412

--HG--
extra : moz-landing-system : lando

build/valgrind/mach_commands.py

@@ -189,9 +189,10 @@ class MachCommands(MachCommandBase):
                              '(reached {timeout} second limit)')
                 elif exitcode != 0:
                     status = 2  # turns the TBPL job red
-                    self.log(logging.ERROR, 'valgrind-fail-errors', {},
-                             'TEST-UNEXPECTED-FAIL | valgrind-test | non-zero exit code'
-                             'from Valgrind')
+                    self.log(logging.ERROR, 'valgrind-fail-errors',
+                             {'exitcode': exitcode},
+                             'TEST-UNEXPECTED-FAIL | valgrind-test | non-zero exit code '
+                             'from Valgrind: {exitcode}')
 
                 httpd.stop()