use zramctl instead, if util-linux deb package is installed

Hi Jonathan,

Maybe you could add this, to make status function get a better look.

NAME       ALGORITHM DISKSIZE  DATA  COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram7 lz4         489,6M  2,8M 291,1K  728K       8 [SWAP]
/dev/zram6 lz4         489,6M  2,8M 224,8K  628K       8 [SWAP]
/dev/zram5 lz4         489,6M  2,8M 270,3K  628K       8 [SWAP]
/dev/zram4 lz4         489,6M  2,8M 378,8K  832K       8 [SWAP]
/dev/zram3 lz4         489,6M  2,8M 292,5K  572K       8 [SWAP]
/dev/zram2 lz4         489,6M  2,5M   268K  692K       8 [SWAP]
/dev/zram1 lz4         489,6M    3M 351,5K  700K       8 [SWAP]
/dev/zram0 lz4         489,6M  2,9M 331,5K  740K       8 [SWAP]

than

compr_data_size: 0 KiB
orig_data_size:  0 KiB
compression-ratio: 0

Cheers,