enable gocritic linter

The linter ensures a common code style.
- use switch/case instead of else if
- use if instead of switch/case for single case statement
- add space between comment and text
- detect the use of defer with os.Exit()
- use short form var += "..." instead of var = var + "..."
- detect problems with append()
```
newSlice := append(orgSlice, val)
```
  This could lead to nasty bugs because the orgSlice will be changed in
  place if it has enough capacity too hold the new elements. Thus we
  newSlice might not be a copy.

Of course most of the changes are just cosmetic and do not cause any
logic errors but I think it is a good idea to enforce a common style.
This should help maintainability.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/define/info.go

@@ -12,7 +12,7 @@ type Info struct {
 	Version    Version                `json:"version"`
 }
 
-//HostInfo describes the libpod host
+// HostInfo describes the libpod host
 type SecurityInfo struct {
 	AppArmorEnabled     bool   `json:"apparmorEnabled"`
 	DefaultCapabilities string `json:"capabilities"`