Description of problem:  User may think it have crashed.

__Example steps to Reproduce:

1. Have a system installed with LUKS encrypted pv for LVM in which you have i.e /, /home, swap...

0. Boot installer, select custom partitioning 

1. Select the encrypted partition, press button to unlock
-> big dialogue window appear

2. enter password, OK
-> The dialogue is replaced by big black area... during about 27 seconds(!) until it is gone and you can continue
- And that is on a modern intel i5 and 256GB nVME SSD !


An experienced user can Ctrl-Alt-F1 and watch the progress of unlocking, listing lv, activating them, etc.   But a normal user may think it have crashed.

So i propose that a message box "Please wait while unlocking and activating..." should appear after hitting that OK button.

Version-Release number of selected component (if applicable): mga 6 installer

(should be checked if valid on cauldron, but i guess so)