Escape backtick from spark-submit arguments

Currently, livy does not escape backticks from user-provided spark-submit arguments. So if a customer is passing any arguments that contain backticks, it will be considered as command substitution during spark-submit causing that argument to become blank or invalid.

Example:
```
--query 'select * from test_db.`test_table`'
```
will become
```
--query 'select * from test_db.'
```

Start by tracing how user-provided arguments are assembled for the spark-submit entry point. Reproduce the issue with the SQL example containing backticks, then add a regression test covering the preserved argument and verify that the existing spark-submit argument tests pass.

Written by the indexing model from the issue text.