apps.common: introduce cache module instead of caching in global variables

src/apps/common/cache.py

@@ -0,0 +1,6 @@
+seed = None
+
+
+def clear():
+    global seed
+    seed = None

src/apps/common/seed.py

@@ -4,8 +4,6 @@ from trezor.crypto import bip39
 
 _DEFAULT_CURVE = 'secp256k1'
 
-_cached_seed = None
-
 
 async def get_root(session_id: int, curve_name=_DEFAULT_CURVE):
     seed = await get_seed(session_id)
@@ -14,10 +12,10 @@ async def get_root(session_id: int, curve_name=_DEFAULT_CURVE):
 
 
 async def get_seed(session_id: int) -> bytes:
-    global _cached_seed
-    if _cached_seed is None:
-        _cached_seed = await compute_seed(session_id)
-    return _cached_seed
+    from . import cache
+    if cache.seed is None:
+        cache.seed = await compute_seed(session_id)
+    return cache.seed
 
 
 async def compute_seed(session_id: int) -> bytes:

src/apps/common/storage.py

@@ -144,8 +144,10 @@ def load_settings(language: str=None,
 
 
 def wipe():
+    from . import cache
     lock()
     config.wipe()
+    cache.clear()
 
 
 def new_device_id() -> str:

tests/run_tests_python_trezor.sh

@@ -31,7 +31,7 @@ not passing:
     test_msg_changepin.py \
     test_msg_ethereum_signtx.py
     test_msg_getaddress_show.py
-    test_msg_loaddevice.py
+    test_msg_loaddevice_xprv.py
     test_msg_ping.py
     test_msg_resetdevice.py
     test_msg_recoverydevice.py
@@ -51,6 +51,7 @@ for i in \
     test_msg_getaddress.py \
     test_msg_getentropy.py
     test_msg_getpublickey.py \
+    test_msg_loaddevice.py
     test_msg_signidentity.py \
     test_msg_signmessage.py \
     test_msg_signtx.py \