ctest: Pass CTEST_SITE/CTEST_BUILD_NAME to configure step

When performing the configure step in dashboard client mode, propagate
`CTEST_SITE` and `CTEST_BUILD_NAME` as the `SITE` and `BUILDNAME`
respective cache variables.

This causes the values recorded in `DartConfiguration.tcl` to match those
specified by the user, allowing subsequent ctest calls to reuse them
automatically.
8 files changed