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/oci_conmon_exec_linux.go

@@ -766,13 +766,11 @@ func prepareProcessExec(c *Container, options *ExecOptions, env []string, sessio
 	if execUser.Uid == 0 {
 		pspec.Capabilities.Effective = pspec.Capabilities.Bounding
 		pspec.Capabilities.Permitted = pspec.Capabilities.Bounding
-	} else {
-		if user == c.config.User {
-			pspec.Capabilities.Effective = ctrSpec.Process.Capabilities.Effective
-			pspec.Capabilities.Inheritable = ctrSpec.Process.Capabilities.Effective
-			pspec.Capabilities.Permitted = ctrSpec.Process.Capabilities.Effective
-			pspec.Capabilities.Ambient = ctrSpec.Process.Capabilities.Effective
-		}
+	} else if user == c.config.User {
+		pspec.Capabilities.Effective = ctrSpec.Process.Capabilities.Effective
+		pspec.Capabilities.Inheritable = ctrSpec.Process.Capabilities.Effective
+		pspec.Capabilities.Permitted = ctrSpec.Process.Capabilities.Effective
+		pspec.Capabilities.Ambient = ctrSpec.Process.Capabilities.Effective
 	}
 
 	hasHomeSet := false