do not exit from postinstall script

This will allow to execute, in a single postinstall, multiple commands.

(From OE-Core rev: 2cd244d6c93ec6d39e2649de64575c365bd4238d)
(From OE-Core rev: b396138ee081c8f5dddbaab0e374787ba2e31029)

Signed-off-by: Sergey Ignatov <sergey_ignatov@mentor.com>
Merge pull request #18 from sergeiignatov/signatov/meip-139_do_not_exit_in_postinstall

do not exit from postinstall script