Let mocked bkill support specific kill signal

[berland]

The tests sent a -s option to the mock that failed the mock. Another error (missing timeout) let the kill test pass when it should not.

Issue
Resolves #7598

Approach
Add timeout to fail the test, then fix the mock and pass the test.

(since the LSF driver does not return the correct return code, the assert on return code did not otherwise fail the test as it would for PBS driver)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure tests pass locally (after every commit!)

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.50%. Comparing base (3469d56) to head (97ad740).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7599      +/-   ##
==========================================
- Coverage   85.19%   84.50%   -0.70%     
==========================================
  Files         384      384              
  Lines       23310    23310              
  Branches      879      877       -2     
==========================================
- Hits        19860    19698     -162     
- Misses       3341     3498     +157     
- Partials      109      114       +5     

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[jonathan-eq]

Very good!👌