CI: Fix finding test script

CI: Fix finding test script

Currently, the run-test code tries to find the package source directory
based on the directory name only. This fails for the Go compiler package
because there is more than one directory named "golang".

This uses the full path listed in the "Source:" line of the control file
to find the package source directory.

This also:

* Checks for the test script earlier, to avoid installing and removing
  ipk files when there is no test script to be run

* Makes PKG_VERSION parsing more lenient, as the package may not have a
  PKG_RELEASE, e.g. attendedsysupgrade-common

Signed-off-by: Jeffery To <redacted>