Revert "Remove QT_HAS_CONNECTIONAGENT define."

This never went in upstream, and never will, as the code is going away (see
following commit/cherry-pick)

This reverts commit 22ab6bab120fcb98058385f49422b4bccd737bde.
remove always ask option.

Jolla removed the always ask option in the UI, which is the reason
for all this code.
Now, if mobile data is autoconnectable, whether roaming or home, it will
be connected.

Change-Id: I6a86315262e8c4c5551b2b2097389559096f14d5
Reviewed-by: Pasi Sjöholm <pasi.sjoholm@jolla.com>
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>