fix(stress_thread): stop assuming current path

[fruch]

cause code assumed HDR to be located on $HOME, in some situations like in the intergation tests of c-s, it wasn't finding it and failing like the following:

FAILED unit_tests/test_cassandra_stress_thread.py::test_01_cassandra_stress -
       invoke.exceptions.UnexpectedExit: Encountered a bad command exit code!

Command: 'cp cs-hdr-write-l1-c0-k1-4bf4051d-abc0-4c0d-840d-f0af5c6b6e8a.hdr
          /home/ubuntu/scylla-cluster-tests/unit_tests/
          cs-hdr-write-l1-c0-k1-4bf4051d-abc0-4c0d-840d-f0af5c6b6e8a.hdr'
Exit code: 1

Stdout:

Stderr:

cp: cannot stat 'cs-hdr-write-l1-c0-k1-4bf4051d-abc0-4c0d-840d-f0af5c6b6e8a.hdr': No such file or directory

Testing

• [ ]

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)
• Add unit tests to cover my changes (under unit-test/ folder)
• Update the Readme/doc folder relevant to this change (if needed)

[dimakr]

LGTM

[fruch]

two intergration tests are failing

10:48:07  FAILED unit_tests/test_config.py::ConfigurationTests::test_24_convert_ami_multi_region - ValueError: Can't convert name 'amzn2-ami-hvm-2.0.20221210.1-x86_64-gp2' to AMI_id, no image found in regions ('eu-west-1', 'eu-west-2', 'us-west-2', 'us-east-1', 'eu-north-1', 'eu-central-1')
10:48:07  FAILED unit_tests/test_config.py::ConfigurationTests::test_25_convert_ami_single_region - ValueError: Can't convert name 'amzn2-ami-hvm-2.0.20221210.1-x86_64-gp2' to AMI_id, no image found in regions ('eu-west-1',)

but it's unrelated, that AMI is remove/deprecated, and we should switch that test into AMI we maintain across all regions

or remove those test, since we are using this functionality for loader and monitor nodes all the time