[IOT-1785] Finish OCF 1.0 identity certificate support

[IOT-1785] Finish OCF 1.0 identity certificate support

Add unit test to exercise certificate provisioning and use
(previously only provisioning was tested).  Fixed bugs in
credresource and ca_adapter_net_ssl. Configure mbedtls to use
 OCF certificate EKUs. Added more logging in many places. Exposed
 API to remove credentials locally for use by test code.

Change-Id: Ia55c7f3a7518f12c99f60280062f156954bdf4ac
Signed-off-by: Greg Zaverucha <gregz@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17983
Reviewed-by: Kevin Kane <kkane@microsoft.com>
Reviewed-by: Dmitriy Zhuravlev <d.zhuravlev@samsung.com>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-by: Nathan Heldt-Sheller <nathan.heldt-sheller@intel.com>