Do not use side-effects of import to initialize hardware plugins

Call HidTransport in the context of a function

plugins/keepkey/keepkey.py

@@ -11,11 +11,25 @@ class KeepKeyPlugin(TrezorCompatiblePlugin):
     libraries_URL = 'https://github.com/keepkey/python-keepkey'
     minimum_firmware = (1, 0, 0)
     keystore_class = KeepKey_KeyStore
-    try:
-        from .client import KeepKeyClient as client_class
-        import keepkeylib.ckd_public as ckd_public
-        from keepkeylib.client import types
-        from keepkeylib.transport_hid import HidTransport, DEVICE_IDS
-        libraries_available = True
-    except ImportError:
-        libraries_available = False
+
+    def __init__(self, *args):
+        try:
+            import client
+            import keepkeylib
+            import keepkeylib.ckd_public
+            import keepkeylib.transport_hid
+            self.client_class = client.KeepKeyClient
+            self.ckd_public = keepkeylib.ckd_public
+            self.types = keepkeylib.client.types
+            self.DEVICE_IDS = keepkeylib.transport_hid.DEVICE_IDS
+            self.libraries_available = True
+        except ImportError:
+            self.libraries_available = False
+        TrezorCompatiblePlugin.__init__(self, *args)
+
+    def hid_transport(self, pair):
+        from keepkeylib.transport_hid import HidTransport
+        return HidTransport(pair)
+
+    def bridge_transport(self, d):
+        raise NotImplementedError('')