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.

Closes #893 (closed)