add empty parameter checking in OCAccountManager

add empty parameter checking in OCAccountManager

Since empty parameter checking for APIs in OCAccountManager is missing,
I added.

And modified signUp API according to the OCF cloud specification.

Change-Id: I23ecc376d3ac6522d411b7a0a9408d79f11fab24
Signed-off-by: Jaewook Jung <jw0213.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11667
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>