How to prevent multiple login windows? Whenever my rMBP wakes up from sleep, it shows a log in page with my user name. The page has a metallic gray background. After I enter my password, another page opens up with my wallpaper along with my user name again, and I have to enter the password one more time.

Output of diskutil list for /dev/disk0 is:

#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *500.3 GB   disk0
1:                        EFI                         209.7 MB   disk0s1
2:                  Apple_HFS Macintosh HD            499.4 GB   disk0s2
3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3


How do I disable multiple login windows each asking for a password when my laptop starts or wakes up from sleep?
Disable File Vault if you don't want this two step log in process. You can be sure FileVault is off by seeing the following from terminal:

Mac:~ me$ diskutil cs list
No CoreStorage logical volume groups found


Alternatively, you could disable and re-enable the File Vault encryption and watch for the prompt where it asks if the OS user should be permitted to unlock the drive with the user's password. 

If you select yes from that, the user will show up on the first login screen and both unlock the FileVault protected volume and log in with the same credentials.