trezor: more user friendly when cannot connect

Tell the user and ask if they want to try again.  If they
say no, raise a silent exception.  Apply this more friendly
behaviour to the install wizard too (see issue #1668).

gui/qt/installwizard.py

@@ -1,4 +1,4 @@
-from sys import stdout
+import sys
 
 from PyQt4.QtGui import *
 from PyQt4.QtCore import *
@@ -14,8 +14,8 @@ from password_dialog import PasswordLayout, PW_NEW, PW_PASSPHRASE
 
 from electrum.wallet import Wallet
 from electrum.mnemonic import prepare_seed
-from electrum.util import SilentException
-from electrum.wizard import (WizardBase, UserCancelled,
+from electrum.util import UserCancelled
+from electrum.wizard import (WizardBase,
                              MSG_ENTER_PASSWORD, MSG_RESTORE_PASSPHRASE,
                              MSG_COSIGNER, MSG_ENTER_SEED_OR_MPK,
                              MSG_SHOW_MPK, MSG_VERIFY_SEED,
@@ -119,7 +119,7 @@ class InstallWizard(QDialog, MessageBoxMixin, WizardBase):
         self.refresh_gui()
 
     def on_error(self, exc_info):
-        if not isinstance(exc_info[1], SilentException):
+        if not isinstance(exc_info[1], UserCancelled):
             traceback.print_exception(*exc_info)
             self.show_error(str(exc_info[1]))
 
@@ -167,7 +167,7 @@ class InstallWizard(QDialog, MessageBoxMixin, WizardBase):
             self.print_error("wallet creation cancelled by user")
             self.accept()  # For when called from menu
         except BaseException as e:
-            self.show_error(str(e))
+            self.on_error(sys.exc_info())
             raise
         return wallet
 

gui/qt/main_window.py

@@ -40,7 +40,7 @@ from electrum.i18n import _
 from electrum.util import (block_explorer, block_explorer_info, format_time,
                            block_explorer_URL, format_satoshis, PrintError,
                            format_satoshis_plain, NotEnoughFunds, StoreDict,
-                           SilentException)
+                           UserCancelled)
 from electrum import Transaction, mnemonic
 from electrum import util, bitcoin, commands
 from electrum import SimpleConfig, COIN_CHOOSERS, paymentrequest
@@ -214,7 +214,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         self.raise_()
 
     def on_error(self, exc_info):
-        if not isinstance(exc_info[1], SilentException):
+        if not isinstance(exc_info[1], UserCancelled):
             traceback.print_exception(*exc_info)
             self.show_error(str(exc_info[1]))