run_remote_tests.sh: make a failure message more meaningful

New message is more suggestive towards the correct approach to
build_packages at least once before one cros_workon starts and tries
running tests.

BUG=none
TEST=none

Change-Id: I5df8e50b25d3838025223c76d3633053a3bdafd9
Reviewed-on: https://gerrit.chromium.org/gerrit/22572
Tested-by: Zdenek Behan <zbehan@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Zdenek Behan <zbehan@chromium.org>
diff --git a/run_remote_tests.sh b/run_remote_tests.sh
index 1b47f1a..5c1a236 100755
--- a/run_remote_tests.sh
+++ b/run_remote_tests.sh
@@ -174,8 +174,9 @@
     AUTOTEST_DIR="/build/${FLAGS_board}/usr/local/autotest"
     if [ ! -d "${AUTOTEST_DIR}" ]; then
       die \
-"Autotest was not emerged. Run emerge-${FLAGS_board} autotest \
-autotest-tests to continue."
+"Autotest was not emerged, ${AUTOTEST_DIR} does not exist. You should \
+initilize it by either running 'build_packages' at least once, or running \
+emerge-${FLAGS_board} autotest autotest-tests."
     fi
     info "Using emerged autotests already installed at ${AUTOTEST_DIR}."
   fi