testimage.bbclass: Fix break introduced with SIGTERM handling
The SIGTERM introduced another break into runexported test,
the handler is in the class TestContext while exporting it
will try to convert the singnal handler to JSON, and this
will throw an exception.
The SIGTERM handler is not needed in the exported test, so this
change will remove the handler before exporting the test. Also
when a test is exported the target is not deployed/started
anymore, it is not necessary.
[YOCTO #8239]
Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
