Use default encryption password if an accessibility service is enabled.

When device is encrypted the user has to authenticate in order to decrypt
the data partition which is required for running accessibility services
and Text-To-Speech. In order to address this issue we are falling back
to use the default password if there is an enabled accessibility service
and the user has secure lock. This will enable the user to authenticate
when accessibility layer is completely functional.

bug:17671790

Change-Id: Iafffe7bcd234008cf91ffb5011b21b803dca227a