Use SecureString where there is data to be cleansed

SecureString has quite a few places it should be used in the user
management code.

Tested: ran set password, test password, and other commands

Change-Id: Ia53bc914d25f7965c3e72d5cf18346e0fa9339b9
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
7 files changed