resize2fs: fix to respect the environment variable E2FSPROGS_FAKE_TIME

resize2fs: fix to respect the environment variable E2FSPROGS_FAKE_TIME

When performing an off-line resize, if an inode's block map needs to
be updated, resize2fs will update the inode's ctime.  In addition, if
inode numbers need to be renumbered due to the file system shrinking
forcing the inode table to be shrunk, any directories which need to be
modified will have their ctime and mtime updated.

If the E2FSPROGS_FAkE_TIME environment variable is set, when the file
system is opened, fs->now will be set to this value, and resize2fs
needs to use it instead of calling time(0) to get their current time.

Addresses-Google-Bug: 230874381
Signed-off-by: Theodore Ts'o <tytso@mit.edu>