Fixed an invalid read/write caused by deleted temporary

Fixed an invalid read/write caused by deleted temporary

The copy used a std::copy mechanism on optionData, which
resulted in the temporary being deleted before the function
returned.  This creates a variable to hold the temporary so that
the string won't be deleted before use.

Change-Id: I5da2601b730e27d42e244b52ba6cdd69a0e28fb4
Signed-off-by: Erich Keane <erich.keane@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1622
Reviewed-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-by: Omkar Hegde <omkar.m.hegde@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>