This will allow diagnosing instances where rados (supposedly) throws exceptions
(supposedly std::error_code).

We do not do a stat before reading. Instead we ask for an arbitrarily big read, and find out
the size of the data while reading. This avoids a race condition in lockfree reads where we failed
to get the full object if it got re-written to a bigger size between stat an read.

Moved XrootCl exception and thrower to cta::exception

common/exception.
Removed tapeserver/castor/exception dir.

cta::exception::TimeOut

cta::exception::OutOfMemory

cta::exception::NotAnOwner

cta::exception::NoPortInRange

cta::exception::NoEntry

cta::exception::MemException

cta::exception::MissingOperand

cta::exception::InvalidConfigEntry

cta::exception::InvalidArgument

cta::exception::EndOfFile

cta::exception::CommandLineNotParsed

cta::exception::BadAlloc

cta::exception::AcceptConnectionInterrupted

Fixed libraby linking which led to multiple initialization of static variable (detected by valgrind's drd).
Worked around cmake's failing dependency management for generated protocol buffer sources (double make in spec file).
Partially fixed the first data transfer session unit test (still disabled).
Fixed a typo in an error message.

Added the retryable error exception and added the catching of different backend exceptions in the frontend

Implementation of the top level retrieve request queueing in Scheduler.

and integrated tpconfig support as well.
Fixed exception losing its initial content after appending with
getMessage() <<

the parsing of cta.conf. Renamed TponfigLines class to Tpconfig.
Unit tested the class.
Fixed message value of Errnum being overwritten when "ex.getMessage() <<"
construct is used on the object.