Fix runtests.sh, broken by commit 3af9e66c12d80.

Exiting with non-zero status breaks runtests.sh.  Add a new --exit-zero
option to parserTests so we still exit 1 for exceptions, but not for
ordinary test failures.

Change-Id: Ib5e9d093b0d29fd567df1acc8f74020275e61411
Merge "Fix runtests.sh, broken by commit 3af9e66c12d80."