mpm/mpmd: Report device state using get_init_status() and verify

When trying to run init(), mpmd will first query the initialization
status of the MPM device. If it is found to be in a bad state, it will
not go forward with initialization, but instead print the error message.

host/lib/usrp/mpmd/mpmd_mboard_impl.cpp

@@ -37,6 +37,15 @@ namespace {
             uhd::rpc_client::sptr rpc,
             const uhd::device_addr_t mb_args
     ) {
+        auto init_status =
+            rpc->request_with_token<std::vector<std::string>>(
+                "get_init_status");
+        if (init_status[0] != "true") {
+            throw uhd::runtime_error(
+                std::string("Device is in bad state: ") + init_status[1]
+            );
+        }
+
         // TODO maybe put this somewhere else?
         const std::set<std::string> key_blacklist{
             "serial", "claimed", "type", "rev", "addr"

mpm/python/usrp_mpm/periph_manager/base.py

@@ -377,11 +377,17 @@ class PeriphManagerBase(object):
         """
         Returns the status of the device after its initialization (that happens
         at startup, not that happens when init() is called).
+        The status is a tuple of 2 strings, the first is either "true" or
+        "false", depending on whether or not the device initialization was
+        successful, and the second is an arbitrary error string.
 
         Use this function to figure out if something went wrong at bootup, and
         what.
         """
-        return self._initialization_status
+        return [
+            "true" if self._device_initialized else "false",
+            self._initialization_status
+        ]
 
     @no_claim
     def list_available_overlays(self):