Speed up linux ocserver to fix apparent instabilities.

Speed up linux ocserver to fix apparent instabilities.

The linux ocserver had three threads running uncluding the main thread.
All three had sleeps in it and there was a delay of 2 seconds between
every call to OCProcess ().
This caused the ocserver to be slow and the server appeared to be
unstable specially when there were many clients sending in requests to
one server.

- Changed ocserver to start the observation thread only when observation
is requested similar to the C++ sample simpleserver.
- Removed the sleep between calls to OCProcess ()
- Moved stopping presence logic to the presence thread from the
  observation thread.

This may be cherrypicked to 1.0.0-dev.

Change-Id: Ib1c9fd732d0973435b556adb8a42610447f1ae7b
Signed-off-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/3339
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>