Bug #1037914: add missing 'growroot' dependencies

Hi. I've managed to reproduce the bug report #1037914 after adding debug to the kernel command line and checking /run/initramfs/initramfs.debug:

+ /scripts/local-bottom/growroot
GROWROOT: /sbin/growpart: 824: /sbin/growpart: grep: not found
GPT PMBR size mismatch (4194303 != 167772159) will be corrected by write.
The backup GPT table is not on the end of the device.
/sbin/growpart: 853: /sbin/growpart: sed: not found
WARN: unknown label
/sbin/growpart: 354: /sbin/growpart: sed: not found
FAILED: sed failed on dump output
/sbin/growpart: 83: /sbin/growpart: rm: not found

After adding the missing dependencies and running sudo update-initramfs -u -k all, the growroot script worked in the next reboot:

+ /scripts/local-bottom/growroot
GROWROOT: CHANGED: partition=1 start=262144 old: size=3930112 end=4192255 new: size=167509983 end=167772126

Can you please review these changes?