Do not create keysets if already exist

[mrochon]

Initialize-IefPolicies creates new policy keys even if they already exist. Change.
Adding key to an existing keyset B2C_1A_TokenSigningKeyContainer.
TokenSigningKeyContainer created/updated
Adding key to an existing keyset B2C_1A_TokenEncryptionKeyContainer.
TokenEncryptionKeyContainer created/updated
Adding key to an existing keyset B2C_1A_FacebookSecret.
New-IEFPoliciesKey: @{code=AADB2C95032; message=One can't mix RSA and Oct types in one key set.; innerError=}
Please wait for the setup to complete...