tests: Collect code coverage separately from each component in vm

tests: Collect code coverage separately from each component in vm

Use a more robust design for collecting the gcov logs from the case
where test cases are run within a virtual machine. This generates a
writable-from-vm build tree for each component separately so that the
lcov and gcov can easily find the matching source code and data files.
In addition, prepare the reports automatically at the end of the
vm-run.sh --codecov execution.

Signed-hostap: Jouni Malinen <j@w1.fi>