sim hot swap: improved error management

Currently, when SIM hot swap fails in either mm-iface or plugin, the
ModemManager still opens ports context and prints a message saying that
SIM hot swap is supported and that it's waiting for SIM insertion,
instead of clearly saying that SIM hot swap is not working.

This patch:

1. introduces a new property MM_IFACE_MODEM_SIM_HOT_SWAP_CONFIGURED
   which is FALSE by default and set to TRUE only when
   setup_sim_hot_swap_finish() succeded.
2. subordinates the completion of SIM hot swap setup (in
   mm-broadband-modem) and the related messages to the the value of
   MM_IFACE_MODEM_SIM_HOT_SWAP_CONFIGURED

Finally, this patch replaces the MBIM's sim_hot_swap_on private property
with the new property MM_IFACE_MODEM_SIM_HOT_SWAP_CONFIGURED, since they have the
same meaning.

plugins/telit/mm-broadband-modem-telit.c

@@ -1377,6 +1377,7 @@ mm_broadband_modem_telit_new (const gchar *device,
                          MM_BASE_MODEM_VENDOR_ID, vendor_id,
                          MM_BASE_MODEM_PRODUCT_ID, product_id,
                          MM_IFACE_MODEM_SIM_HOT_SWAP_SUPPORTED, TRUE,
+                         MM_IFACE_MODEM_SIM_HOT_SWAP_CONFIGURED, FALSE,
                          NULL);
 }