wpa_supplicant: Add 'SCAN TYPE=ONLY' functionality

Usual manual scan request may cause reassociation due to several reasons.
New command is intended to perform pure scan.

Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>

Change-Id: I67d06265fc99ffee802d509410de5c8431c8c43a
Merge branch 'cm-10.2' into martincz