Reenable IPCA unit tests.

Reenable IPCA unit tests.

Fix: https://jira.iotivity.org/browse/IOT-1960

Address a couple of items:
Make a snapshot of vector variables for calling back to apps to address
issue with vector update in the middle of callbacks.

Also, properly delete observe handles in the mock library when app
cancels resource observation.  Otherwise the unit tests slow down as
number of test iteration increases.

Change-Id: I0116deb534ddfaa8e29b84a942ba3d95c1986816
Signed-off-by: Soemin Tjong <stjong@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18181
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>