[buteo-syncfw] Emit network error if session is not open in less than 10secs

In some conditions Qt network layer can take some time to fail,
since msyncd runs as a background process is not desirable to wait
long for a network request reply, with this PR if no reply comes in 10secs
a network error is emitted.
Merge pull request #34 from nemomobile/keepalive

[buteo-syncfw] Emit network error if session is not open in less than 10secs