modified searchUser() API on OCAccountManager

modified searchUser() API on OCAccountManager

Since the account server spec has been changed, it needs some modifications.
 - modified uri "/oic/account/user" to "/oic/account/search"
 - modified query form to search more than one user.
 - removed searchUser() API for searching a specific user.

Change-Id: I431d6a4750d7a0772831da1865de2e8c5498ed09
Signed-off-by: Jaewook Jung <jw0213.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/14545
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Jee Hyeok Kim <jihyeok13.kim@samsung.com>