lxc-checkconfig fails on ArchLinux

Hi, 

On ArchLinux, lxc-checkconfig fails:

```
$ lxc-checkconfig 
--- Namespaces ---
Namespaces: zgrep -q CONFIG_NAMESPACES=[y|m] /proc/config.gz

gzip: stdout: Broken pipe
required
Utsname namespace: zgrep -q CONFIG_UTS_NS=[y|m] /proc/config.gz

gzip: stdout: Broken pipe
missing
Ipc namespace: zgrep -q CONFIG_IPC_NS=[y|m] /proc/config.gz

gzip: stdout: Broken pipe
required
Pid namespace: zgrep -q CONFIG_PID_NS=[y|m] /proc/config.gz

gzip: stdout: Broken pipe
required
User namespace: zgrep -q CONFIG_USER_NS=[y|m] /proc/config.gz
missing
Network namespace: zgrep -q CONFIG_NET_NS=[y|m] /proc/config.gz

gzip: stdout: Broken pipe
missing
Multiple /dev/pts instances: zgrep -q DEVPTS_MULTIPLE_INSTANCES=[y|m] /proc/config.gz
enabled
...
```

This is because `zgrep -q` is mysteriously failing:

```
$ zgrep -q 'CONFIG_VLAN_8021Q=[y|m]' /proc/config.gz

gzip: stdout: Broken pipe
```
```
$ zgrep  'CONFIG_VLAN_8021Q=[y|m]' /proc/config.gz
CONFIG_VLAN_8021Q=m
```