Format shutter speed correctly

Previously, ExifInterface would return a value, n, while the actual
format for shutter speed is 1/(2^n). This change adds a helper method
that formats shutter speed before displaying it to the user.

Bug: 64083610
Test: In place
Change-Id: I4980099c54eb342a4d5fb8fd1cb8bc371aba013c
3 files changed