run_ptest.sh: Clean TEST_TARGETS before build image
run_ptest.sh: Clean TEST_TARGETS before build image

Remove native and nativesdk out of TEST_TARGETS before add it
to IMAGE_INSTALL.
'bitbake core-image-minimal' will fail if there are native or nativesdk
packages in package list.

Signed-off-by: Trung Do <64081e6b7eb2b24289b8a4e51cef9836ddf28af2@toshiba-tsdv.com>

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