Fix trailing whitespace mismatch error when running 02-test_errstr.

Fix trailing whitespace mismatch error when running 02-test_errstr.

Fixes #12449

On a aix7_ppc32 machine the error was of the form
match 'Previous owner died ' (2147483743) with one of ( 'Previous owner died', 'reason(95)' )
Stripping the trailing whitespace from the system error will address this issue.

Suggested fix by @pauldale.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12451)