new keytool.html changes for jDK-8010125

Some modifications to keytool.html:
 
1. Change the command line usage from
 
   {-srcalias srcalias {-destalias destalias} [-srckeypass srckeypass] [-destkeypass destkeypass] }
 
to
 
   {-srcalias srcalias {-destalias destalias} [-srckeypass srckeypass]} [-destkeypass destkeypass]
 
which means -destkeypass can be set without -srcalias being present.
 
2. Add a note to the -importkeystore command after the existing line:
 
   The destination entry will be protected using destkeypass. If destkeypass
   is not provided, the destination entry will be protected with the source
   entry password.
+ For example, most 3rd-party tools require storepass and keypass in a PKCS #12
+ keystore to be the same. In order to create a PKCS #12 keystore for these
+ tools, always specify a -destkeypass to be the same as -deststorepass.