Make -edgeHost option mandatory
Make -edgeHost option mandatory

The 'flag' package does not technically allow options without
default values being set, so strictly speaking this is implemented
in a 'the default value is not viable' case (namely, the empty string).

mikepea/cdn-acceptance-tests,mikepea/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,mikepea/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,alphagov/cdn-acceptance-tests,mikepea/cdn-acceptance-tests