Better error message for wrong keystore password when using keystore API

[pablomendezroyo]

Importing a keystore using the keymanager API with the correct password results in the following response

response: {"data":[{"status":"imported","message":null}]}

Importing a keystore using the keymanager API with the wrong password results in the following response

response: {"data":[{"status":"error","message":"Error importing keystore: Unable to add validator"}]}

The error message for the wrong password import should add more detailed information, such as

response: {"data":[{"status":"error","message":"Error importing keystore: Unable to add validator, wrong password provided"}]}