C++ - Unit-test compilation on Windows fixes

Issue 1:
thrift\lib\cpp\test\concurrency\ThreadFactoryTests.h uses <unistd.h> for usleep().

Replaced usleep() with THRIFT_SLEEP_USEC() and removed inclusion of unistd.h

Issue 2:
static const double ERROR;
macro ERROR already defined in wingdi.h

Replaced with TEST_ERROR, but perhaps it is better to find it more better name.

PR: https://github.com/apache/thrift/pull/207