HPCC-9415 New epoll implementation with common base class

Signed-off-by: Mark Kelly <mark.kelly@lexisnexis.com>
HPCC-9415 Disable by default for now

Signed-off-by: Mark Kelly <mark.kelly@lexisnexis.com>
HPCC-9415 Use epoll, fix critical section around init

Signed-off-by: Mark Kelly <mark.kelly@lexisnexis.com>
Merge pull request #4957 from mckellyln/hpcc9415x

HPCC-9415 Use epoll_wait instead of select in data loop

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>