qmp-shell: learn to send commands with quoted arguments

qmp-shell: learn to send commands with quoted arguments

Use shlex to split the CLI command, respecting quoted arguments, and
also comments. This allows to call for ex:

(QEMU) human-monitor-command command-line="screendump /dev/null"
{"execute": "human-monitor-command", "arguments": {"command-line": "screendump /dev/null"}}

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180326150916.9602-3-marcandre.lureau@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>