`rundir = "."` should not be required for IT tests

[apesternikov]

currently the canonical way for IT tests to locate the setup binary is through

data = [
   ":target_it.setup"
],
args = [
   "-setup",
   "$(location :target_it.setup")",
],

which also require

rundir = "."

in go tests because the default current working dir for go tests is the test source directory to be compatible with the non-bazel way of running tests.
IT setup target should be able to locate runfiles if test is started with or without rundir parameter.