Make Camera2 DCIM-compliant [2/2]

According to DCF specification (http://www.schnarff.com/file-formats/exif/dcf.PDF),
directory names in DCIM should follow the following conventions:
∙ The directory name is 8 characters in length.
∙ The first three characters are a number between "100" and "999"; numbers "000"
through "099" shall not be used. This number is referred to as the directory
number.
∙ The rest of the name after the directory number shall be five characters. These are
referred to here as the DCF directory name Free characters.
∙ These five characters consist only of the upper-case alphanumeric characters
shown in Table 1-1. They shall not contain two-byte characters or special codes.

This is a second part that makes Gallery properly display "DCIM/100ANDRO" as a
"Camera" album.

Change-Id: I526b99a0ec57ed0f1f4509341db6618f32a1168c