crtools: fix exit code for page-server

cr_page_server() returns pid, if it is executed as a daemon
otherwise it returns an error code.

crtools returns 0 only if cr_page_server() returns a positive value,
what is obviously wrong.

travis-ci: success for crtools: close a signal descriptor after passing a preparation stage (rev6)
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>