Make provider password lookup more flexible

This patch allows passwords that are passed to a resource
to be looked up from a method on the provider.

This allows parent classes to override this method for cases
where passwords may need to be decrypted by the provider.
Remove define iscsi_send_target

This class did nothing, added no value, and
only served to make things more complicated,
I have removed it, and made appropriate changes
to calling conetentn.
Merge pull request #21 from bodepd/decrypt_part_two

Decrypt part two