Do not rely on default dig options in system tests

Do not rely on default dig options in system tests

Some system tests assume dig's default setings are in effect.  While
these defaults may only be silently overridden (because of specific
options set in /etc/resolv.conf) for BIND releases using liblwres for
parsing /etc/resolv.conf (i.e. BIND 9.11 and older), it is arguably
prudent to make sure that tests relying on specific +timeout and +tries
settings specify these explicitly in their dig invocations, in order to
prevent test failures from being triggered by any potential changes to
current defaults.