tests/ports/unix: Improve skip detection for os.getenv and time module.

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

tests/ports/unix/mod_os.py

@@ -1,6 +1,9 @@
 # This module is not entirely compatible with CPython
 import os
 
+if not hasattr(os, "getenv"):
+    print("SKIP")
+    raise SystemExit
 
 os.putenv("TEST_VARIABLE", "TEST_VALUE")
 

tests/ports/unix/time_mktime_localtime.py

@@ -1,4 +1,8 @@
-import time
+try:
+    import time
+except ImportError:
+    print("SKIP")
+    raise SystemExit
 
 DAYS_PER_MONTH = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]