TEST: regression test for CVM-667
FIX: SignatureManager::LoadPublicRsaKeys() can ignore broken keys
TEST: adapt for restrictive version
SignatureManager::LoadPublicRsaKeys() fails on broken keys
FIX: logging flags for new error messages
FIX: inconsistent test case naming
Merge pull request #545 from reneme/fix-ignore_malformed_pubkeys

FIX: Broken Public Key FIle Prevents all Mounts

This changes the behaviour of SignatureManager::LoadPublicRsaKeys() to be a bit more permissive. If one ore more public key files cannot be read successfully, they are just skipped. If the list of public keys is not empty but none was read successfully, it will still produce an error.

Additionally this contains a regression test for the issue described in CVM-667.