[wifi-manager] Issue scan request based on last scan type.

[wifi-manager] Issue scan request based on last scan type.

When scan is requested by application but previous scan is already
in progress at connman then hold new scan request till scan-done
signal of previous scan is received.
On receiving scan-done signal, wifi-manager extract last scan type.
- If last scan type is same as new scan type and scan is done for full
channel then do not start fresh scan and send scan results of last
scan to applications.
- In all other scenarios start fresh scan for new scan type.

Change-Id: I2d171611707c5508c1aa60bcf150579cf192fbf8
Signed-off-by: Niraj Kumar Goit <niraj.g@samsung.com>