security: Refactoring creation of SecPublicInfo and SecTpm during KeyChain creation

The objective of this refactoring is to allow KeyChains with custom PIB
and TPM.  As of this commit, KeyChain no longer hard-codes PIB and TPM
instance creation.  Instead, creation is delegated to factory functions,
which need to be statically registered, e.g., using
`NDN_CXX_KEYCHAIN_REGISTER_PIB` and `NDN_CXX_KEYCHAIN_REGISTER_TPM`
macros.

Change-Id: I0d29b5ed8d74d99d8a56c4a6e9024f2587dd125e
Refs: #2384
diff --git a/src/security/sec-tpm.cpp b/src/security/sec-tpm.cpp
index d8c6a4f..a4b27f1 100644
--- a/src/security/sec-tpm.cpp
+++ b/src/security/sec-tpm.cpp
@@ -43,7 +43,7 @@
 std::string
 SecTpm::getTpmLocator()
 {
-  return this->getScheme() + m_location;
+  return this->getScheme() + ":" + m_location;
 }
 
 ConstBufferPtr