Store clusters password in secure location

[nirs]

Keeping cluster password in clear text is ok for test clusters but for real clusters it is better
to store the password in the system encrypted container used for other passwords.

Go Keyring library seems to do what we need.

Possible implementation:

• make the password field optional
• if password is not set, get the password from the keyring during login

Questions:

• Who will store the password into the keyring?
• Password key - cluster url?