phosphor-gpio-presence: Add expected method for CLI11

The Phosph-gpio-presence@.service template has a --drivers and
--extra-ifaces which can be empty in some configurations[1].
systemd will end up launching the process with an extra empty
argument. CLI11 will fail unless we give an explicit
"--drivers=<value> or --extra-ifaces=<value>".
Add the expected method to --drivers and --extra-ifaces to limit the
number of incoming parameters for parameters.

Observed in hardware testing:
```
--drivers: 1 required TEXT missing
Run with --help for more information.
```

[1] https://github.com/openbmc/openbmc/blob/master/meta-facebook/meta-bletchley/recipes-phosphor/gpio/phosphor-gpio-monitor/obmc/gpio/presence-sled1.conf

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Iab8da95d88843652e657933656d9121b43311655
diff --git a/presence/main.cpp b/presence/main.cpp
index aa1eb24..3e94b85 100644
--- a/presence/main.cpp
+++ b/presence/main.cpp
@@ -80,15 +80,17 @@
                    "Object path under inventory that will be created")
         ->required();
     app.add_option(
-        "-d,--drivers", drivers,
-        "List of drivers to bind when card is added and unbind when card is removed\n"
-        "Format is a space separated list of path,device pairs.\n"
-        "For example: /sys/bus/i2c/drivers/some-driver,3-0068");
+           "-d,--drivers", drivers,
+           "List of drivers to bind when card is added and unbind when card is removed\n"
+           "Format is a space separated list of path,device pairs.\n"
+           "For example: /sys/bus/i2c/drivers/some-driver,3-0068")
+        ->expected(0, 1);
     app.add_option(
-        "-e,--extra-ifaces", ifaces,
-        "List of interfaces to associate to inventory item\n"
-        "Format is a comma separated list of interfaces.\n"
-        "For example: /xyz/openbmc_project/.../1,/xyz/openbmc_project/.../2");
+           "-e,--extra-ifaces", ifaces,
+           "List of interfaces to associate to inventory item\n"
+           "Format is a comma separated list of interfaces.\n"
+           "For example: /xyz/openbmc_project/.../1,/xyz/openbmc_project/.../2")
+        ->expected(0, 1);
 
     /* Parse input parameter */
     try