Install packages before airgapping

Installing ip6tables after disrupting IPv4 traffic will fail utterly if
the machine uses IPv4 for package installations. Install both packages
in lockstep before actually disrupting any traffic.

Fixes: e6bb827 ("Whitelist local IPv6 CIDRs when airgapping nodes")
Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

inttest/common/airgap.go

@@ -155,10 +155,10 @@ localAddrs:
 
 func (a *Airgap) airgapMachine(ctx context.Context, name, v4CIDRs, v6CIDRs string) error {
 	const airgapScript = `
+		apk add --no-cache %s
 		v4Cidrs='%s'
 		v6Cidrs='%s'
 		if [ -n "$v4Cidrs" ]; then
-			apk add --no-cache iptables
 			for cidr in $v4Cidrs; do
 				iptables -A INPUT -s $cidr -j ACCEPT
 				iptables -A OUTPUT -d $cidr -j ACCEPT
@@ -168,7 +168,6 @@ func (a *Airgap) airgapMachine(ctx context.Context, name, v4CIDRs, v6CIDRs strin
 		fi
 
 		if [ -n "$v6Cidrs" ]; then
-			apk add --no-cache ip6tables
 			for cidr in $v6Cidrs; do
 				ip6tables -A INPUT -s $cidr -j ACCEPT
 				ip6tables -A OUTPUT -d $cidr -j ACCEPT
@@ -183,6 +182,18 @@ func (a *Airgap) airgapMachine(ctx context.Context, name, v4CIDRs, v6CIDRs strin
 		fi
 	`
 
+	var packages []string
+	if v4CIDRs != "" {
+		packages = append(packages, "iptables")
+	}
+	if v6CIDRs != "" {
+		packages = append(packages, "ip6tables")
+	}
+
+	if len(packages) < 1 {
+		return nil
+	}
+
 	a.Logf("Airgapping %s", name)
 
 	ssh, err := a.SSH(ctx, name)
@@ -192,6 +203,6 @@ func (a *Airgap) airgapMachine(ctx context.Context, name, v4CIDRs, v6CIDRs strin
 	defer ssh.Disconnect()
 
 	return ssh.Exec(ctx, "sh -e -", SSHStreams{
-		In: strings.NewReader(fmt.Sprintf(airgapScript, v4CIDRs, v6CIDRs)),
+		In: strings.NewReader(fmt.Sprintf(airgapScript, strings.Join(packages, " "), v4CIDRs, v6CIDRs)),
 	})
 }