Simplify exception naming

[111pontes]

Currently, exception names are language specific (e.g. YCPPServiceProviderError for C++ vs. YPYServiceProviderError for Python). Language-independent names should be used to be consistent with the language-independent notation used throughout the YDK API (e.g. YServiceProviderError instead of YCPPServiceProviderError). A language may have language specific exceptions if needed in particular cases, but language-independent naming should be preferred in general.