Env variables from Maven properties overwrite generated keystore password

[scottkurz]

It seems wrong that using a property like -Dliberty.env.xyz=123 overwrites the keystore password generated into server.env, by default.

This isn't a new problem and we've already worked out a solution: #648.
But the use of the mergeServerEnv=true parameter requires a more advanced user who reads the plugin doc.

Let me propose taking another pass at this. What if we said:

DESIGN

IF
(mergeServerEnv=false AND Env Maven Props exist AND (there's neither server.env in configDirectory NOR a serverEnvFile parm)
THEN we merge special properties (of now, just one, "keystore_password") from the target/install server.env into the maven env props that we're going to write, preferring a property in maven env props if there is one.

Yes.. we lose symmetry by special casing one variable..but it seems important enough to justify IMHO.

I thought about just issuing a warning but it seems like you'd have to go through some trouble to read server.env every time to determine if this case needs a warning or not.