Low: asterisk: remove -v flag from sipsak invocation

sipsak injects 0x0d characters in its output that ocf_run
doesn't cope too well with. So, remove the -v flag for now
and just log sipsak's error code.

See this thread for the related ocf_run discussion:
http://lists.linux-ha.org/pipermail/linux-ha-dev/2011-November/019032.html