Made suffix length of rotated logcat files constant.

The suffix now uses as many digits as needed to cover the maximum number
of rotated files.

eg, for 20 files it would use 2 digits: log_file.{01,02,03,...,20}

Change-Id: I4709b3cf4bf88c209db3c4d9e24a3a4731c98bae
Merge "Made suffix length of rotated logcat files constant."