installer: confusion of set/get disk encryption passphrase dialogs
Currently, the installer uses the same dialog to "set" and "get" the passphrase for disk encryption, which causes some confusion, as well as a bit inconvenience.
The followings are the 2 cases to come across the confusing "get" passphrase dialog:
1. installation finished, begins to configure the system, which will ask the disk encryption passphrase;
2. boot into the LiveCD, and use it to "Configure an installed System" (see attached screenshots).
The corresponding code is at "usr.sbin/installer/dfuibe_installer/fn_configure.c" with the function "fn_get_passphrase()". It may be better to create separate functions for the "set" and "get" passphrase dialogs, respectively.