Crash happens if back button is pressed during "Format as Portable"

SD card format as internal, during migrate process press back key or  During "Format as Portable", 
press back key crash happened.

Fix:
Hide the bottom navigation from that particular activity so that user can not accidentally 
press back key.
/packages/apps/Settings/src/com/android/settings/deviceinfo/StorageWizardFormatProgress.java
/packages/apps/Settings/src/com/android/settings/deviceinfo/StorageWizardMigrateProgress.java

Bug: 238596768
Test:
1. Insert sdcard or generate virtual disk using command : adb shell "sm set-virtual-disk true"
2. Go to Settings -> Storage -> SD Card -> Format as Internal -> move later
3. After step 1, back to storage
4. Again enter in Storage -> SD Card -> to do migrate data
5. during migrate process press back key
6. Storage -> SD Card -> Format as Portable
7. During "Format as Portable", press back key

Change-Id: I1f393ffb872bb90d7dfeb4e1c86648b3413645a1