Trezor/KeepKey: force watching only improvements

Only warn about watching only once given a chance to pair.
Failure to pair makes watching-only and warns.
In error message to user, distinguish between failure to connect
and failure to pair.

plugins/hw_wallet/hw_wallet.py

@@ -39,26 +39,29 @@ class BIP44_HW_Wallet(BIP44_Wallet):
         # handler.  The handler is per-window and preserved across
         # device reconnects
         self.handler = None
-        self.force_watching_only = True
+        self.force_watching_only = False
 
     def set_session_timeout(self, seconds):
         self.print_error("setting session timeout to %d seconds" % seconds)
         self.session_timeout = seconds
         self.storage.put('session_timeout', seconds)
 
+    def set_force_watching_only(self, value):
+        if value != self.force_watching_only:
+            self.force_watching_only = value
+            self.handler.watching_only_changed()
+
     def unpaired(self):
         '''A device paired with the wallet was diconnected.  This can be
         called in any thread context.'''
         self.print_error("unpaired")
-        self.force_watching_only = True
-        self.handler.watching_only_changed()
+        self.set_force_watching_only(True)
 
     def paired(self):
         '''A device paired with the wallet was (re-)connected.  This can be
         called in any thread context.'''
         self.print_error("paired")
-        self.force_watching_only = False
-        self.handler.watching_only_changed()
+        self.set_force_watching_only(False)
 
     def timeout(self):
         '''Called when the wallet session times out.  Note this is called from

plugins/trezor/plugin.py

@@ -20,9 +20,6 @@ from ..hw_wallet import BIP44_HW_Wallet, HW_PluginBase
 # TREZOR initialization methods
 TIM_NEW, TIM_RECOVER, TIM_MNEMONIC, TIM_PRIVKEY = range(0, 4)
 
-class DeviceDisconnectedError(Exception):
-    pass
-
 class TrezorCompatibleWallet(BIP44_HW_Wallet):
 
     def get_public_key(self, bip32_path):
@@ -137,17 +134,15 @@ class TrezorCompatiblePlugin(HW_PluginBase):
         assert self.main_thread != threading.current_thread()
 
         devmgr = self.device_manager()
-        client = devmgr.client_for_wallet(self, wallet, force_pair)
+        try:
+            client = devmgr.client_for_wallet(self, wallet, force_pair)
+        except:
+            wallet.set_force_watching_only(True)
+            raise
 
         if client:
             self.print_error("set last_operation")
             wallet.last_operation = time.time()
-        elif force_pair:
-            msg = (_('Could not connect to your %s.  Verify the '
-                     'cable is connected and that no other app is '
-                     'using it.\nContinuing in watching-only mode '
-                     'until the device is re-connected.') % self.device)
-            raise DeviceDisconnectedError(msg)
 
         return client