method_call and method_reply of type error are mutually exclusive. ell
will never forward method_reply messages to dbus services, so checking
for dbus_message_has_error is pointless.
Previously, command_option_get used to return NULL in the following
two scenarios: when command-line option with a such name didn’t exists
or its argument was not provided. This worked great for the cmd-line
options with the required arguments. With introduction of the cmd-line
options with no or optional arguments the function was changed to return
a boolean value indicating the existence of a such option and then, if
it had an argument - value_out variable would have been set.
Thereafter, this patch modifies the current usages of command_option_get.
Note, in these particular applications of command_option_get there is no
need to check the returned value from command_option_get, since these
options have the required arguments and we can only check if the value_out
parameter has been set or not.
