mke2fs: Add extended option to select quota type

mke2fs: Add extended option to select quota type

mke2fs was creating both user and group quota inodes on enabling
the quota feature. This patch adds the extended option 'quotatype'
that can be used to exclusively specify the quota type that the
user wants to initialize.

 # Ex: Default behavior without extended option creates both
 # user and group quota inodes:
 $ mke2fs -t ext4 -O quota /dev/ram1

 # To enable only user quotas:
 $ mke2fs -t ext4 -O quota -E quotatype=usr /dev/ram1
 # To enable only group quotas:
 $ mke2fs -t ext4 -O quota -E quotatype=grp /dev/ram1

Signed-off-by: Aditya Kali <adityakali@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>