make icedtea7-native to be able to use shared state

icedtea-native encodes absolute build time classpaths which wont
work in sstate however at same time we can override it with env
variables like BOOTCLASSPATH and LD_LIBRARY_PATH to reflect current
build environment.

Secondly, exclude ICEDTEA_PARALLEL_MAKE from shared state signatures, it
can alter signatures if PARALLEL_MAKE value between producer and
consumer of sstate is not matching.

Now that icedtea7-native is shared state safe, remove the shared state
invalidation on jamvm-native that was needed for icedtea7-native to
build

Signed-off-by: Khem Raj <raj.khem@gmail.com>