lib/live/build/lb_binary_disk failed with "lzcat: : Invalid filename suffix" on Ubuntu 16.04

[Ｖ字龍(Vdragon)]

As title, I believe it's because that the command missing --suffix option.

Also the xz(1) manpage mentions that:

```
When writing scripts that need to decompress files, it is recommended to always use the name xz with appropriate arguments (xz -d or xz -dc) instead of the names unxz and xzcat.

```

We should follow the recommendation, but that's another bug

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: live-build 3.0~a57-1ubuntu25
Uname: Linux 4.4.0-pf8-buo-ren-pf-intel-haswell-and-gcc-autodetect-optimized x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Apr 17 16:50:58 2016
InstallationDate: Installed on 2016-01-07 (100 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
PackageArchitecture: all
SourcePackage: live-build
UpgradeStatus: Upgraded to xenial on 2016-04-07 (9 days ago)