Add ESP certificate bundle feature

Adds the ESP certificate bundle feature that enables users to bundle a
root certificate bundle together with their application.

Default bundle includes all Mozilla root certificates

Closes IDF-296

components/mbedtls/esp_crt_bundle/test_gen_crt_bundle/entrust.pem

@@ -0,0 +1,26 @@
+Entrust Root Certification Authority
+====================================
+-----BEGIN CERTIFICATE-----
+MIIEkTCCA3mgAwIBAgIERWtQVDANBgkqhkiG9w0BAQUFADCBsDELMAkGA1UEBhMCVVMxFjAUBgNV
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+-----END CERTIFICATE-----
+

components/mbedtls/esp_crt_bundle/test_gen_crt_bundle/invalid_crt.pem

@@ -0,0 +1,26 @@
+Entrust Root Certification Authority
+====================================
+-----BEGIN CERTIFICATE-----
+MIIEkTCCA3mgAwIBAgIERWtQVDANBgkqhkiG9w0BAQUFADCBsDELMAkGA1UEBhMCVVMxFjAUBgNV
+BAoTDUVudHJ1c3QsIEluYy4xOTA3BgNVBAsTMHd3dy5lbnRydXN0Lm5ldC9DUFMgaXMgaW5jb3Jw
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+-----END CERTIFICATE-----
+

components/mbedtls/esp_crt_bundle/test_gen_crt_bundle/test_gen_crt_bundle.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python
+
+import unittest
+import sys
+import os
+
+try:
+    import gen_crt_bundle
+except ImportError:
+    sys.path.append("..")
+    import gen_crt_bundle
+
+
+idf_path            = os.environ['IDF_PATH']
+ca_crts_path        = idf_path + '/components/mbedtls/esp_crt_bundle/'
+test_crts_path      = idf_path + '/components/mbedtls/esp_crt_bundle/test_gen_crt_bundle/'
+
+ca_bundle_bin_file  = 'x509_crt_bundle'
+
+der_test_file       = 'baltimore.der'
+pem_test_file       = 'entrust.pem'
+verified_der_bundle = 'baltimore_crt_bundle'
+verified_pem_bundle = 'entrust_crt_bundle'
+invalid_test_file   = 'invalid_crt.pem'
+ca_crts_all_file    = 'cacrt_all.pem'
+
+
+class Py23TestCase(unittest.TestCase):
+
+    def __init__(self, *args, **kwargs):
+        super(Py23TestCase, self).__init__(*args, **kwargs)
+        try:
+            self.assertRaisesRegex
+        except AttributeError:
+            # assertRaisesRegexp is deprecated in Python3 but assertRaisesRegex doesn't exist in Python2
+            # This fix is used in order to avoid using the alias from the six library
+            self.assertRaisesRegex = self.assertRaisesRegexp
+
+
+class GenCrtBundleTests(Py23TestCase):
+
+    # Verify generation from der vs known certificate
+    def test_gen_from_der(self):
+        bundle = gen_crt_bundle.CertificateBundle()
+        bundle.add_from_file(test_crts_path + der_test_file)
+
+        crt_bundle = bundle.create_bundle()
+
+        with open(test_crts_path + verified_der_bundle, 'rb') as f:
+            verified_bundle = f.read()
+
+        self.assertEqual(crt_bundle, verified_bundle)
+
+    # Verify generation from pem vs known certificate
+    def test_gen_from_pem(self):
+        bundle = gen_crt_bundle.CertificateBundle()
+        bundle.add_from_file(test_crts_path + pem_test_file)
+
+        crt_bundle = bundle.create_bundle()
+
+        with open(test_crts_path + verified_pem_bundle, 'rb') as f:
+            verified_bundle = f.read()
+
+        self.assertEqual(crt_bundle, verified_bundle)
+
+    def test_invalid_crt_input(self):
+        bundle = gen_crt_bundle.CertificateBundle()
+
+        with self.assertRaisesRegex(gen_crt_bundle.InputError, "Invalid certificate"):
+            bundle.add_from_file(test_crts_path  + invalid_test_file)
+
+        with self.assertRaisesRegex(gen_crt_bundle.InputError, "No certificate found"):
+            bundle.add_from_pem("")
+
+
+if __name__ == "__main__":
+    unittest.main()