[IOT-830] Added remove API for all credentials on |credresource|

[IOT-830] Added remove API for all credentials on |credresource|

added all credentials remove API for iotivity client with provisioning
feature. considering commercialization, iotivity client needs not only to
reset SVR data, e.g. doxm, acl and cred resources, but also to remove only
all credential data for its owned servers. for the former case legacy API(s)
could be supported but for the latter case additional API is needed.
the added API for this supports to remove all credentials and update
persistent storage in running iotivity client.
Jira-issue: https://jira.iotivity.org/browse/IOT-830

Change-Id: Icbfab415469bea72caf7a759f6437503bf76dafd
Signed-off-by: Kyungsun Cho <goodsun.cho@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4377
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sachin Agrawal <sachin.agrawal@intel.com>