[ArmZabbixAPI][DBTablesUser] Remove unused variables
[AMQPConsumer] Remove an unsed constant "DEFAULT_TIMEOUT"
[server][test] Remove unused variables
[ClosureBase] Remove needless "virtual" keyword

This commit fixes a following warning by clang:

./Closure.h:144:7: warning: 'Signal0::connect' hides overloaded virtual function
      [-Woverloaded-virtual]
        void connect(Closure0 *closure)
[Helper] Don't use reference type for the argument of _assertStringVectorVA()

This commit fixes the following compiler warning:

  Helpers.cc:52:19: warning: 'va_start' has undefined behavior with reference types [-Wvarargs]
          va_start(valist, actual);
                         ^
  /usr/bin/../lib/clang/3.4/include/stdarg.h:33:52: note: expanded from macro 'va_start'
  #define va_start(ap, param) __builtin_va_start(ap, param)
                                                     ^
  Helpers.cc:48:48: note: parameter of type 'const StringVector &' (aka 'const vector<std::string> &') is declared here
  void _assertStringVectorVA(const StringVector &actual, ...)
Merge pull request #863 from project-hatohol/fix-compile-warnings-3

Fix compile time warnings