We keep support for the pty based monitor so that we can re-connect
to VMs started by older versions of libvirtd.
* src/domain_conf.c: handle formatting and parsing unix monitors
* src/qemu_driver.c: add qemudOpenMonitorUnix(), remove the monitor
pty path searching from qemudFindCharDevicePTYs(), switch
qemudStartVMDaemon() and qemuDomainXMLToNative() to using a unix
monitor
* tests/qemuxml2argvtest.c: switch to using a unix monitor
* tests/qemuxml2argvdata/qemuxml2argv-*.args: update test data
virExec will write out the pid of the daemonized process only. Use this
in the QEMU driver, rather than QEMU's pidfile, so we can catch errors we
might miss if the emulator bails early.
