Allow users to change their own password/key

Users were not able to update their own password/key
with the update operation resulting in 403 (HTTPForbidden).

EXAMPLES:
Command to update password/key of regular user:
gswauth-add-user -U account1:user1 -K old_pass account1 user1 new_pass

Command to update password/key of account admin:
gswauth-add-user -U account1:admin -K old_pass -a account1 admin new_pass

Command to update password/key of reseller_admin:
gswauth-add-user -U account1:radmin -K old_pass -r account1 radmin new_pass

Signed-off-by: Prashanth Pai <ppai@redhat.com>
Merge pull request #61 from prashanthpai/update-password

Allow users to change their own password/key