Fixing FileProvider for read key from kubernetes secret file

[gawsoftpl]

There was a issue for Kubernetes secrets: I saved key in file as string not binary file.

Kubernetes save secrets without whitelines and converted string to binary

For that situation I have error: Invalid ciphertext because script read string file as binary and do not convert them from string(hex2bin) and do not remove whitespaces.

1. I moved string convert function to Util class
2. I wrote unit tests for binary, string files with key
3. I add new logic for getSymmetricKey in FileProvider