Set additional info for LaunchBrowser error case.

A recent change in 3GPP TS 31.124 27.22.4.26 spec for
LAUNCH BROWSER SEQ 1.6. expects an additional info
'Default URL unavailable' incase where default url
is not set.

Fix: In CatService, while handling the Launch Browser
error response include the additonal info 'Default
URL unavailable'.

3GPP Ref link:
http://www.etsi.org/deliver/etsi_ts/131100_131199/131124/
13.02.00_60/ts_131124v130200p.pdf

Change-Id: Idb80c1b8f36749a0ad6e5d53c7a4ac693917d884
CRs-Fixed: 1002699