fix error in tests when /bin/sh is not bash

== is a bashism, we should use = for /bin/sh; this prevents output like:

/home/ubuntu/criu/test/post-dump.sh: 3: [: post-dump: unexpected operator
/home/ubuntu/criu/test/post-dump.sh: 3: [: network-unlock: unexpected operator
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/post-dump.sh

 #!/bin/sh
 
-[ "$CRTOOLS_SCRIPT_ACTION" == post-dump ] || exit 0
+[ "$CRTOOLS_SCRIPT_ACTION" = post-dump ] || exit 0
 
 #
 # Special code to inform zdtm that we're