qga: copy argument strings

Following patch will return allocated strings, so we must correctly
initialize alloc & free them. The nice side effect is that we no longer
have to check for "fixed_state_dir" to call ga_install_service() with a
NULL state dir. The default values are set after parsing the command
line options.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
