Add @seconds variable to qemuAgentSend().
When @timemout is true, @seconds controls how long to wait for a
response (if @seconds is VIR_DOMAIN_QEMU_AGENT_COMMAND_DEFAULT,
default to QEMU_AGENT_WAIT_TIME).
In addition, @seconds must be >= 0 or VIR_DOMAIN_QEMU_AGENT_COMMAND_DEFAULT.
If @timeout is false, @seconds is ignored.
Signed-off-by: NMATSUDA Daiki <matsudadik@intellilink.co.jp>