Reply with short device name in meta-data requests.
Fixes for: EUCA-8637
Don't dump stack trace back to user for undefined meta-data entries.
Fixes for: EUCA-7886, EUCA-9739, EUCA-7842
Map ephemeral0 to 'sdb' for HVM and 'sda2' for paravirtualized image.
Fixes for: EUCA-7860
Added comments for about root device name