Mark uncovered path in interface

Improve the coverage numbers by marking an untested path as
not having coverage.

Signed-off-by: Joshua Lock <jlock@vmware.com>

Author: joshuagl

securesystemslib/interface.py

@@ -55,7 +55,7 @@
   from colorama import Fore
   TERM_RED = Fore.RED
   TERM_RESET = Fore.RESET
-except ImportError:
+except ImportError: # pragma: no cover
   logger.debug("Failed to find colorama module, terminal output won't be colored")
   TERM_RED = ''
   TERM_RESET = ''