Bluetooth: shell: Improve attribute discovery callback

This patch makes attributes discovery more easier from the point
of shell application user.
UUIDs of discovered attribute declarations are now printed.
For services handle range is shown.

btshell> gatt-discover-primary 1800
btshell> Service 1800 found: start handle 00000001, end_handle 0000000b

Characteristic properties are parsed to string and printed
with characteristic value handle.

Characteristic f000ffc1-0451-4000-b000-000000000000 found: handle 0000006a,
				value_handle 0000006b
Properties: [write][write w/w rsp][notify]

Change-Id: I6823fa562206ccf336dc301ee71bc4a02cecc14f
Signed-off-by: Mariusz Skamra <mariusz.skamra@tieto.com>