tools: export: MCUXpresso: fix case inconsistencies in .templ file names

The templ file names are both all upper case and lower case letters.
The Target Names map is usually all upper case. The match could fail
if the templ file, as we have case-sensitive comparison. Handle such
cases by perorming a case-insensitve check.

mbed export of a project to MCUXpresso could potentially always fail
irrespective of what is passed in -m option since the target names
map entry and the filename may not match. This commit fixes this issue.

Example of the issue that this commit fixes:

$ mbed export -i mcuxpresso -m lpc11u68 -v
<snip>
project.py: error: LPC11U68 not supported by mcuxpresso
<snip>

tools/export/mcuxpresso/__init__.py

@@ -1,6 +1,6 @@
 """
 mbed SDK
-Copyright (c) 2011-2016 ARM Limited
+Copyright (c) 2011-2019 ARM Limited
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -28,9 +28,10 @@ from builtins import str
 import copy
 import tempfile
 import shutil
+import re
 
 from subprocess import Popen, PIPE
-from os import getcwd, remove
+from os import getcwd, remove, listdir
 from os.path import splitext, basename, exists
 from random import randint
 
@@ -54,10 +55,19 @@ class MCUXpresso(GNUARMEclipse):
 
     MBED_CONFIG_HEADER_SUPPORTED = True
 
+    @staticmethod
+    def is_target_name_in_dir(path, target_name):
+        # toos/export/mcuxpresso/ has entries with
+        # both lower and upper case. Handle these inconsistencies.
+        for entry in listdir(path):
+            if(re.match(entry, target_name + '_cproject.tmpl', re.IGNORECASE)):
+                return True
+        return False
+
     @classmethod
     def is_target_supported(cls, target_name):
         # target is supported when *_cproject.tmpl template file exists
-        if exists(cls.TEMPLATE_DIR + '/mcuxpresso/' + target_name + '_cproject.tmpl'):
+        if MCUXpresso.is_target_name_in_dir(cls.TEMPLATE_DIR + '/mcuxpresso/', target_name):
             target = TARGET_MAP[target_name]
             return apply_supported_whitelist(
                 cls.TOOLCHAIN, POST_BINARY_WHITELIST, target)