exec: properly handle exec replies

when using exec on replies, populate the reply code and reason instead of
R-URI variables

(cherry picked from commit 7e5bbcf4e522eece1222cb49d2a69790a9992957)

Conflicts:
	modules/exec/exec_hf.c

(cherry picked from commit e6a36b5324e18c3f473b393b1290f2af3e29868a)