munet: fix bug in cli.py

[liambrady]

When a target node and command share the same same substring in host_cmd_split, then an incorrect index will be used. This results in returning a bad command.

For example, define the following in munet.yaml:

topology:
  nodes:
    - name: shoo
    - name: foo
cmd:
  commands:
    - name: ""
      exec: "bash -c \"{}\""
      format: "[NODE ...] COMMAND [ARGUMENT ...]"
      interactive: true

and the following results can be observed:

munet> foo sh echo hi
hi
munet> shoo sh echo hi
*** non-zero exit status: 127
/bin/bash: line 1: oo: command not found
munet>

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.83%. Comparing base (6345948) to head (f9a2da7).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
- Coverage   59.98%   58.83%   -1.15%     
==========================================
  Files          19       19              
  Lines        5665     5728      +63     
==========================================
- Hits         3398     3370      -28     
- Misses       2267     2358      +91     

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