RFR (12): 8212669: Add note to Cipher javadoc about using full transformation and not relying on defaults

[Sean Mullan]

Please review this javadoc-only change to the Cipher class. An @apiNote 
has been added to each of the getInstance methods to recommend that the 
full transformation be specified when creating a Cipher and to avoid 
relying on the defaults. Also a link to the defaults used by the JDK 
providers has been added as an @implNote.

webrev: http://cr.openjdk.java.net/~mullan/webrevs/8212669/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8212669
Thanks,
Sean