Description of problem:
With https://github.com/RedHatInsights/insights-core/pull/1855 we added logging of the client versions to the insights-client.log but the path we specify is incorrect and will fail on RHEL8 systems which do not have python installed.  The correct path should be /usr/libexec/platform-python.

Version-Release number of selected component (if applicable):
This was introduced in 3.0.112-1

How reproducible:
100%

Steps to Reproduce:
1. Set up a  which does not have python2 or python3 installed
2. Excecute insights-client --register
3. Weep

Actual results:
# insights-client 
Fatal error
Traceback (most recent call last):
  File "/var/lib/insights/last_stable.egg/insights/client/phase/v1.py", line 32, in _f
    func(client, config)
  File "/var/lib/insights/last_stable.egg/insights/client/phase/v1.py", line 131, in post_update
    print_egg_versions()
  File "/var/lib/insights/last_stable.egg/insights/client/utilities.py", line 262, in print_egg_versions
    env={'PYTHONPATH': egg, 'PATH': os.getenv('PATH')}, stdout=PIPE, stderr=STDOUT)
  File "/usr/lib64/python3.6/subprocess.py", line 729, in __init__
    restore_signals, start_new_session)
  File "/usr/lib64/python3.6/subprocess.py", line 1364, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'python': 'python'
Starting to collect Insights data for my-rhel8-system-without-python


Expected results:
same, but with less tracebacking because no one wants to see that. Also the version isn't being logged, which was the motivation when introducing this bug.

Additional info:
The quality engineering group is sorry that we let this bug escape and will do better in the future.