lib/sysfs: allow to write to sysfs attributes

Signed-off-by: Karel Zak <kzak@redhat.com>
lib/ismounted: make it more compatible with lsblk output

Signed-off-by: Karel Zak <kzak@redhat.com>
zrmactl: add new command to control /dev/zramN devices

Co-Author: Timofey Titovets <nefelim4ag@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>