[vector] RFR:8244269: vector api tests crashed with "assert(is_location()) failed: must be"

[Viswanathan, Sandhya]

Please find below a webrev which cleans up the slice(), unslice() and iotaShuffle() implementations and fixes the assert(is_location()).

http://cr.openjdk.java.net/~sviswanathan/vectorIntrinsics/8244269/webrev.00/

27 of the 29 Vector API test failures with -Xcomp pass with this patch.

The remaining two are a different assert and will be taken up separately.

Best Regards,
Sandhya