Undetectable vegeta installation results in cryptic error

[mattsse]

local version detection is broken if vegeta is missing

python3 -m flood version --json

will return 1 if which vegeta fails:

flood/flood/ops/installation_utils.py

Line 19 in 03f93c4

result = subprocess.check_output(['which', 'vegeta'])

this raises an exception if vegeta is not installed.

resulting in a cryptic error

packages/flood/tests/load_tests/load_test_runs.py", line 308, in _run_load_test_remotely
    remote_flood_version = remote_installation['flood_version']
                           ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
TypeError: 'int' object is not subscriptable

perhaps this command can be wrapped in a try statement and raise an error for missing vegeta?