[autotest] Force |num=7| on network3g.

dynamic_suite will fail to schedule network3g with |num| less than 7 due
to the number of non-subsetting HostSpecs being greater than |num|,
which currently defaults to 6.

TEST=run ./run_suite.py -s network3g with -u less than 7, fails
TEST=run ./run_suite.py -s network3g with -u equal to 7, succeeds
BUG=None

Change-Id: Ibaa3e45d2bd609a05819a601ca6e3e7533e211f4
Reviewed-on: https://gerrit.chromium.org/gerrit/36604
Commit-Ready: Alex Miller <milleral@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Tested-by: Alex Miller <milleral@chromium.org>
1 file changed