tests/multi_net: Require SSL cert file to be available for test to run.

These were missed in 2bba507148 because they
didn't use the `os.stat` pattern.

Signed-off-by: Damien George <damien@micropython.org>

tests/multi_net/sslcontext_server_client.py

@@ -14,14 +14,10 @@ PORT = 8000
 certfile = "ec_cert.der"
 keyfile = "ec_key.der"
 
-try:
+with open(certfile, "rb") as cf:
-    with open(certfile, "rb") as cf:
+    cert = cadata = cf.read()
-        cert = cadata = cf.read()
+with open(keyfile, "rb") as kf:
-    with open(keyfile, "rb") as kf:
+    key = kf.read()
-        key = kf.read()
-except OSError:
-    print("SKIP")
-    raise SystemExit
 
 
 # Server

tests/multi_net/sslcontext_server_client_ciphers.py

@@ -14,14 +14,10 @@ PORT = 8000
 cert = cafile = "ec_cert.der"
 key = "ec_key.der"
 
-try:
+with open(cafile, "rb") as f:
-    with open(cafile, "rb") as f:
+    cadata = f.read()
-        cadata = f.read()
+with open(key, "rb") as f:
-    with open(key, "rb") as f:
+    keydata = f.read()
-        keydata = f.read()
-except OSError:
-    print("SKIP")
-    raise SystemExit
 
 
 # Server

tests/multi_net/sslcontext_verify_callback.py

@@ -15,14 +15,10 @@ PORT = 8000
 cert = cafile = "ec_cert.der"
 key = "ec_key.der"
 
-try:
+with open(cafile, "rb") as f:
-    with open(cafile, "rb") as f:
+    cadata = f.read()
-        cadata = f.read()
+with open(key, "rb") as f:
-    with open(key, "rb") as f:
+    key = f.read()
-        key = f.read()
-except OSError:
-    print("SKIP")
-    raise SystemExit
 
 
 def verify_callback(cert, depth):

tests/multi_net/tls_dtls_server_client.py

@@ -13,14 +13,10 @@ PORT = 8000
 certfile = "ec_cert.der"
 keyfile = "ec_key.der"
 
-try:
+with open(certfile, "rb") as cf:
-    with open(certfile, "rb") as cf:
+    cert = cadata = cf.read()
-        cert = cadata = cf.read()
+with open(keyfile, "rb") as kf:
-    with open(keyfile, "rb") as kf:
+    key = kf.read()
-        key = kf.read()
-except OSError:
-    print("SKIP")
-    raise SystemExit
 
 
 # DTLS server.