Doc changes for JDK-8138653

Default keysizes have been updated as part of JDK-8138653, so the security guides need to be updated:

1. http://docs.oracle.com/javase/8/docs/technotes/guides/security/crypto/HowToImplAProvider.html

Key Pair Generators
"For example, the Diffie-Hellman key pair generator supplied by the SunJCE provider uses a default prime modulus size (keysize) of 1024 bits."

s/1024/2048/

Algorithm Parameter Generators
"For example, the SunJCE provider uses a default prime modulus size (keysize) of 1024 bits for the generation of Diffie-Hellman parameters"

s/1024/2048

Default Initializations
"and the "SunJCE" provider uses a default modulus size (keysize) of 1024 bits for the generation of Diffie-Hellman parameters."

"For example, the DSA key pair generator in the Sun provider supplies a set of pre-computed p, q, and g default values for the generation of 512, 768, and 1024-bit key pairs."

s/and 1024-bit/1024, and 2048-bit/

2. http://docs.oracle.com/javase/8/docs/technotes/guides/security/SunProviders.html

Keysize Restrictions
In the table for RSA for SunRsaSign provider, change the default (2nd column) from 1024 to 2048.

In both tables for Diffie-Hellman for SunJCE provider, change the default (2nd column) from 1024 to 2048.

In the table for RSA for SunMSCAPI provider, change the default (2nd column) from 1024 to 2048.