[IOT-1785] Support for Certificate Provisioning

[IOT-1785] Support for Certificate Provisioning

- Shell script to create IoTivity identity certificates using
OpenSSL command line tools.
- Partial unit test for providing credentails to the CA adapter
layer.  Tests loading of PEM cert and key.
- Misc changes and fixes to the cred resource
- updated provisioning client to provision certs
- helper code to create certs from CSRs

Change-Id: I7d3ab4810c7f7d6247ed90420cb97cbdb5f829a4
Signed-off-by: Greg Zaverucha <gregz@microsoft.com>
Signed-off-by: Kevin Kane <kkane@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17509
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>