Phone: Ignore touch during network operators search

When network search is in progress, the progress dialog is
dismissed if user taps the screen. This in-turn cancels
manual search and switches to the previous screen.
This behavior can be avoided if the dialog property is set
to ignore user touch events.
If required BACK key can be used to cancel search and move
to previous screen.

Change-Id: I00da1dfec78498d2f35f6bb5d49e42bb3ad43cc2
CRs-Fixed: 367631
NetworkSettings: Cannot dismiss progress dialog sometimes.

When "Load Network List" dialog is shown, move
NetworkSettings activity to backgroud by pressing
HOME key. After several minutes, go to
NetworkSettings again. Network list is shown under
the progress dialog, but user cannot dismiss the
Progess dialog.

Steps to reproduce this issue:
1) Settings->wireless & networks->mobile networks;
2) Press "network operators";
3) "Searching" progress dialog is shown;
4) Press HOME key to return to home;
5) Wait several minutes;
6) Goto "network operators" activity again.

Expected result: "Searching" dialog is dismissed;
Actual result: "Searching" dialog is still shown.

Change-Id: Ib411a89be2bcf907e6cca4c1d5693f8445f2d681
Signed-off-by: Bin Li <libin@marvell.com>