Enhancement: add the capability to use a non local user for remote actions

[MarbolanGos]

Hello,

Here is a case I am facing with milkcheck and i would like your view on an enhancement I made, with a very quick testing (only with remote: yes at the moment). In my case, all checks are being run as root (as usual) but due to security concerns, some tests must be achieved via a specific SIMPLE_USER which is reachable via the root ssh keys.

In a first attempt, I changed the config files to do:

cmd: "su -l %SIMPLE_USER -c 'ls'"

This is not very simple to maintain... In order to be simpler, I wanted to add an option to a service for being run as the SIMPLE_USER.

I did a modification in the code which seems to fit my needs but must be reviewed as I am not at all expert in python...

[MarbolanGos]

Just an example:

[root@admin-node ~]# milkcheck --report=full -c /root/test_milkcheck step0 -n pm-mgt0
step0 test-mgt ran in 0.20 s
 > pm-mgt0: uid=2001(admin) gid=2001(admin) groups=2001(admin)
 > pm-mgt0 exited with 1
test-mgt - Test                                                                                            [  ERROR  ]

 SUMMARY - 1 action (1 failed)
 + test-mgt.step0 - Test
    Target: pm-mgt0
    Command: id && exit 1
# cat /root/test_milkcheck/test.yaml 
---
services:
    test-mgt:
        fanout: 324
        timeout: 30
        desc: Test
        target: "pm-mgt0"
        ssh_user: "admin"
        actions:
            step0:
                cmd: "id && exit 1"