abrt-action-save-package-data: properly close rpm database. Closes #674.

RPM library uses Berkeley DB, which emits warnings like this
if DB files weren't closed properly:

 BDB2053 Freeing read locks for locker 0x1e0: 28718/139661746636736

This change fixes it.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Jakub Filak <jfilak@redhat.com>