PkClient: Successfully return when calling pk_client_adopt_async

[tintou]

We had no way to return a PkResults in the correct path.

Closes #709

[sidt4]

I think #709 is fixed with this PR, but now we get a exit code: unknown for each PK transaction.

/281_ccdedeee	role         get-updates
/281_ccdedeee	sender       /usr/bin/gnome-software
/281_ccdedeee	status       finished
/281_ccdedeee	exit code: unknown
/282_eeaaecaa	allow_cancel 1
/282_eeaaecaa	percentage   100
/282_eeaaecaa	role         get-details
/282_eeaaecaa	sender       /usr/bin/gnome-software
/282_eeaaecaa	status       query
/282_eeaaecaa	status       finished
/282_eeaaecaa	exit code: unknown
/283_abdbaeeb	allow_cancel 1
/283_abdbaeeb	percentage   -1
/283_abdbaeeb	role         get-updates
/283_abdbaeeb	sender       /usr/bin/gnome-software
/283_abdbaeeb	status       wait
/283_abdbaeeb	status       finished
/283_abdbaeeb	exit code: unknown

Sample expected output:

Transactions:
 1	/450_addddedd
/450_addddedd	allow_cancel 1
/450_addddedd	percentage   -1
/450_addddedd	role         get-updates
/450_addddedd	sender       /usr/bin/gnome-software
/450_addddedd	status       setup
/450_addddedd	percentage   39
/450_addddedd	percentage   91
/450_addddedd	percentage   100
/450_addddedd	status       finished
Transactions:
 [none]
/450_addddedd	exit code: success
Transactions:
 1	/451_ddcbbcbc
/451_ddcbbcbc	allow_cancel 1
/451_ddcbbcbc	percentage   -1
/451_ddcbbcbc	role         get-details
/451_ddcbbcbc	sender       /usr/bin/gnome-software
/451_ddcbbcbc	status       setup
/451_ddcbbcbc	percentage   100
/451_ddcbbcbc	status       finished
/451_ddcbbcbc	exit code: success
Transactions:
 [none]

[sidt4]

This issue is addressed in #756. Thanks !