Check if bootmode tests were skipped before teardown

If we decided to skip the bootmode tests, it means the device didn't have enough capabilities (non-support, or a single display mode) for them to be meaningful. It also means:

* We never poked at the apis, so we don't need to clean up our own usage, and
* If boot modes aren't supported, then cleaning ourselves up will report errors from these apis, which would cause the tests to fail.

So, just skip teardown if the test was also skipped.

Bug: 389190752
Flag: EXEMPT test only
Test: this
Change-Id: Ida7635f1da540251196e9af2d060962cfeed72fc