[M40] Switch to trunk's webrtc and libjingle_source_talk repo.

[M40] Switch to trunk's webrtc and libjingle_source_talk repo.

Updated .gclient and sync_repo.sh to get newly added trunk repositories
instead of upstream's: s-webrtc.git and s-libjingle_source_talk.git.

In addition, to deal with any future repo additions, patch adds an
additional step to check the existing repo url in target path against
the desired repo url and remove the path if the two urls do not match.

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=8410
Reviewed by: Kangil Han, Piotr Tworek, SeungSeop Park

Change-Id: I8b9fd9499a3e1433c43bd4685e9821b60331a5d3
Signed-off-by: SeungSeop Park <sns.park@samsung.com>